Sourdough Japanese Tuna Mayo and Seaweed Seasoning Rounds

Name: Sourdough Japanese Tuna Mayo and Seaweed Seasoning Rounds
Prep time: 15 min
Cook time: 12 min
Total time: 27 min
Yield: 12 servings
Cuisine: Japanese
Ingredients: 1 cup (240 ml) sourdough discard, active and bubbly, at room temperature; 5 oz (142 g) canned tuna in water, drained very well; 3 tablespoons (45 g) Japanese or regular mayonnaise; ½ teaspoon (2½ ml) soy sauce; ½ teaspoon (2½ ml) mirin; 1 tablespoon (3 g) aonori (dried seaweed powder); 1 tablespoon (6 g) green onion, finely chopped (optional); ½ teaspoon (1½ g) white sesame seeds, toasted, optional (optional)

From the MyKitchenBank Kitchen

Crispy-edged sourdough discard crackers topped with a savory Japanese-style tuna and mayo mixture, finished with aonori seaweed seasoning. These rounds are quick to make, perfect for snacking or serving as appetizers, and a delicious way to use sourdough starter discard.

Prep: 15 min
Cook: 12 min
Wait: 5 min
Total: 32 min
Makes: 24 rounds (2 per serving)

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Steps

Before you start

Preheat your oven to 400°F (200°C) and line two baking sheets with parchment paper
Have your sourdough discard at room temperature and ready to use
Drain the canned tuna very well in a fine sieve to remove excess liquid

1
Prepare tuna mixture
- In a small bowl, combine the drained tuna, mayonnaise, soy sauce, mirin, and chopped green onion (if using).
- Mash with a fork until well combined but still slightly chunky, about 1 minute.
- Set aside.
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Ready when: mixture is evenly combined with small flakes of tuna visible
Tip: Don't overmix—keep some texture in the tuna for better flavor and mouthfeel.
2
Shape discard rounds
- Spread the sourdough discard in a thin, even layer on the two prepared baking sheets, aiming for about ¼-inch (6 mm) thickness.
- Using a 1-inch (2.5 cm) round cookie cutter or the rim of a small glass, cut out rounds by pressing straight down—do not twist, as twisting seals the edges and prevents rising.
- You should get about 24 rounds total.
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Ready when: clean-cut rounds across both sheets
Tip: Press the cutter straight down, then lift away—twisting traps air and creates a too-dense round.
3
Bake base roundsOven 400°F / 205°C
- Place the baking sheets in the preheated 400°F (200°C) oven and bake for 8–10 minutes, until the rounds are light golden and just starting to crisp at the edges, but still soft enough to top.
- They will firm up further after cooling.
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Ready when: light golden color on top and bottoms, very slightly firm but still pliable
Tip: Don't overbake at this stage—the rounds will crisp up more with the topping and residual heat.
4
Cool slightly
- Remove the baking sheets from the oven and let the rounds cool for 2–3 minutes on the sheets.
- They should still be warm and slightly pliable.
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Ready when: rounds are no longer piping hot but still warm to the touch
5
Top with tuna mixture
- Using a small spoon or piping bag, place about ½ teaspoon of the tuna mixture on top of each round, pressing gently so it adheres.
- Space the rounds slightly apart on the sheets.
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Ready when: all rounds are evenly topped
Tip: Don't overfill—a small dollop is enough. Overfilling will cause the topping to slide off during the final bake.
6
Return to oven and finishOven 400°F / 205°C
- Return the topped rounds to the 400°F (200°C) oven for 2–3 minutes just to warm through.
- Remove and immediately dust each round with a small pinch of aonori (about ⅛ teaspoon per round) and a few sesame seeds if using.
- The residual heat will help the aonori adhere.
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Ready when: topping is warm, aonori clings to the surface
Tip: Add aonori right after removing from heat—the warmth helps it stick and distributes the flavor better.
7
Cool and serve
- Let the rounds cool on the baking sheets for 2 minutes, then transfer to a serving plate or platter.
- Serve at room temperature or while still slightly warm.
- The rounds will continue to crisp as they cool.
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Ready when: rounds are set and crispy on the outside, warm or at room temperature
Tip: Serve within 30 minutes of completion for the best crispy-tender texture.

Good to know

Tips

Japanese mayonnaise (like Kewpie) has a higher egg yolk content and creates a creamier, richer topping than standard American mayo. Use it if available for more authentic flavor.
Aonori has a delicate, grassy flavor and can lose potency with heat. Add it after baking so its fresh seaweed taste shines through.
For a spicy kick, mix ¼ teaspoon of sriracha or wasabi into the tuna mixture. It pairs beautifully with the aonori.
These rounds are best served within 30 minutes of completion. They soften over time as the tuna mixture releases moisture, so serve at a gathering rather than making far ahead.

Storage & reheating

Store cooled rounds in an airtight container at room temperature for up to 3 hours. They are best served fresh and warm. Do not refrigerate or freeze, as the sourdough rounds will become soggy. If made ahead, store the baked unfilled rounds in an airtight container and top just before serving.

Substitutions

aonori (dried seaweed powder) → furikake seasoning (Japanese mixed seasoning blend). Furikake contains seaweed, sesame, bonito flakes, and dried fish—use the same amount and skip the sesame seed topping to avoid duplication.
canned tuna in water → fresh tuna, finely minced (3 oz by weight). Use sashimi-grade tuna if available. Mix raw tuna with the mayo and seasonings for a fresher taste, but consume on the day it is made.
Japanese or regular mayonnaise → Greek yogurt mixed with a touch of sesame oil (2 tablespoons yogurt + ½ teaspoon sesame oil). This creates a lighter, tangier topping. The sesame oil adds authentic flavor.
sourdough discard, active and bubbly → store-bought sourdough, thinly sliced and cut into 1-inch rounds. Skip the initial spreading and cutting step. Toast the rounds lightly in a 375°F oven for 5 minutes, then top and finish as directed.