Mushroom and Gruyère Panini
A French-inspired grilled cheese sandwich with sautéed cremini mushrooms, melted Gruyère, and fresh thyme on crispy sourdough. The mushrooms are cooked until golden and caramelized, creating a rich umami-forward filling that pairs beautifully with the nutty cheese. Quick enough for a weeknight lunch, elegant enough to serve to guests.
- Prep
- 5 min
- Cook
- 14 min
- Wait
- 3 min
- Total
- 22 min
- Makes
- 2 panini sandwiches
Steps
Before you start
- Have a panini press ready, or set up a large skillet with a heavy spatula
- Slice the mushrooms thin (about ¼ inch) so they cook and brown quickly
- Remove the Gruyère from the fridge about 10 minutes before starting—it's easier to slice when slightly less cold
- Read through both grilling methods so you're ready to move quickly once the pan heats
Slice mushrooms and dice shallot
- Slice the cremini mushrooms into about ¼-inch-thick slices (you should have about 8 oz / 225g total).
- Finely dice the shallot into small, even pieces, about ⅛ inch.
- Chop the fresh thyme leaves.
- Slice the Gruyère cheese into thin pieces (or grate it on a box grater).
- Have all ingredients prepped and within reach before you start cooking—you'll be moving quickly once the pan heats up.
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Ready when: All vegetables are uniformly cut and ready to cook; cheese is sliced or grated
Tip: Slicing the mushrooms thin (about ¼ inch) ensures they cook through quickly and brown evenly. Prep everything before you start cooking so the shallot doesn't overcook.
Heat butter and cook shallot
- Place a large skillet over medium-high heat.
- Add 2 tablespoons of unsalted butter and let it melt.
- When the butter is foaming and just beginning to smell nutty (about 30 seconds to 1 minute), add the diced shallot.
- Stir occasionally with a wooden spoon until the shallot is softened and just beginning to turn golden at the edges, about 1 minute.
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Ready when: Shallot is softened, translucent, and fragrant
Tip: Watch the butter carefully—you want it nutty, not brown or burnt. If it's browning too fast, reduce the heat slightly and take the pan off the heat briefly.
Add mushrooms and cook until golden
- Add all the sliced mushrooms to the skillet and increase the heat to high.
- Cook, stirring occasionally, for 6-8 minutes.
- The mushrooms will first release a lot of liquid; keep cooking until that liquid has completely evaporated and the mushrooms are golden brown and tender.
- There should be no pooled liquid remaining in the pan.
- The mushrooms should have browned, caramelized spots on them.
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Ready when: Mushrooms are golden brown and tender; the pan is nearly dry with no visible liquid
Tip: Resist stirring too often—let the mushrooms sit undisturbed for 30-second intervals so they can brown and develop flavor. If they're sticking, reduce heat to medium-high.
Season filling and let cool
- Remove the skillet from the heat.
- Stir in the chopped fresh thyme and season to taste with salt and freshly ground black pepper.
- Let the mushroom mixture cool in the pan for 2-3 minutes.
- This cooling time allows the mushrooms to firm up slightly so they won't leak out of the sandwich when you assemble and grill it.
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Ready when: Mushrooms are still warm but cool enough to touch the pan comfortably
Tip: The mushroom filling can be made up to 2 hours ahead and stored at room temperature, covered. Gently reheat it in the skillet over low heat for 1-2 minutes just before assembling if needed.
Layer cheese, mushrooms, and bread
- Lay the 4 slices of sourdough bread on a cutting board.
- If using Dijon mustard, lightly spread about ½ teaspoon on the inside of each slice.
- On two of the slices, layer in this order: about half the Gruyère cheese (roughly 1.5 oz / 45g), all of the cooled sautéed mushrooms (about 4-5 oz / 120g), then the remaining Gruyère cheese (another 1.5 oz / 40g).
- Top each with a remaining bread slice, mustard-side down.
- Press gently with your hand to secure the layers and ensure good contact between ingredients.
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Ready when: Sandwiches are stacked, pressed gently, and sturdy enough to handle
Tip: Spreading mustard on both bread slices helps bind the filling and adds pungent contrast to the earthy mushrooms and nutty cheese. Don't overfill—the mushrooms should be in a single layer.
Toast and press the paniniOven 350°F / 175°C
- Choose your grilling method: PANINI PRESS METHOD: Preheat the panini press to high heat (about 2-3 minutes).
- Spread the remaining 1 tablespoon of softened butter on the outside of both sandwiches—cover all exposed bread surfaces on top and bottom.
- Place each sandwich in the preheated press and close.
- Cook for 3-4 minutes (175°C or 350°F) until the bread is deep golden brown and crispy and you can feel the cheese oozing slightly when you gently press the sandwich.
- The bread should be caramelized and crunchy, not just lightly toasted.
- SKILLET METHOD: Heat a large skillet or griddle over medium-high heat until a drop of water sizzles immediately (about 2 minutes).
- Spread the remaining 1 tablespoon of butter on the outside of both sandwiches (all exposed bread surfaces).
- Carefully place both sandwiches in the skillet and immediately press down firmly with a spatula or the bottom of a heavy pot.
- Cook undisturbed for 2-3 minutes until the bread is golden and crispy on the first side.
- Carefully flip the sandwiches and cook the other side for 2-3 minutes until golden and the cheese is fully melted inside (you may hear it sizzle as the cheese melts).
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Ready when: Bread is golden brown and crispy on both sides; cheese is fully melted and beginning to ooze slightly at the edges
Tip: Don't move the sandwich during the first minute of cooking—let it sit undisturbed so it develops a crispy, caramelized crust. If the outside is browning too fast while the inside is still cold, reduce heat slightly and cook longer.
Cut and serve hot
- Transfer the paninis to a cutting board and let rest for 1-2 minutes.
- This short rest allows the melted cheese to set slightly so it doesn't run out immediately when you cut.
- Slice each panini diagonally in half and serve immediately while still hot, with the oozing cheese visible in the center.
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Ready when: Panini has rested and is ready to cut
Good to know
Tips
- Don't overcrowd the skillet or panini press. If you're making more than 2 sandwiches, work in batches so the bread browns properly and the cheese melts evenly.
- If the outside of the bread is browning too quickly while the cheese inside is still cold, reduce the heat to medium and cook a bit longer for more even melting.
- The key to a great panini is pressing it firmly and letting it sit undisturbed for the first minute of cooking to develop a golden, crispy crust.
- Freshly grated Gruyère will melt faster and more evenly than pre-sliced cheese; it's worth shredding it yourself if you have a box grater.
Make ahead
The mushroom filling can be cooked up to 2 hours ahead, covered, and kept at room temperature. Gently reheat in a skillet over low heat for 1-2 minutes before assembling and grilling. The entire panini can be assembled up to 30 minutes ahead and kept at room temperature before grilling, though the bread will dry out slightly.
Storage & reheating
Room temperature: Eat immediately; leftover panini becomes soggy within 1 hour. Refrigerator: Store in an airtight container for up to 2 days. Reheat in a skillet over medium heat for 2-3 minutes per side, pressed with a spatula, until the bread is crispy and the cheese re-melts. Freezer: Not recommended; the bread becomes tough and the texture of the mushrooms deteriorates when frozen and thawed.
Substitutions
- Gruyère cheese → Swiss, Emmental, or Fontina cheese. Use nutty, semi-firm cheeses that melt beautifully. Avoid soft cheeses like Brie that ooze too quickly.
- cremini mushrooms → portobello, oyster, or button mushrooms. Use the same weight; button mushrooms will cook slightly faster since they're more delicate.
- fresh thyme → ½ teaspoon dried thyme, or fresh rosemary or oregano. Dried herbs are more concentrated; reduce fresh quantities by half when substituting.
- sourdough bread → whole wheat, rye, or ciabatta bread. Ciabatta will give a crispier result; whole wheat will be more earthy and nutty.
