Mentai Mochi Cheese Gratin Recipe

Make a light dashi: combine 400 ml water with 8 g instant dashi granules (or prepare kombu-katsuobushi dashi: 400 ml water, 5 cm kombu soaked 30 min then simmered and removed, 10 g katsuobushi strained). Keep warm.

In a small saucepan over medium heat, add the warm dashi, 1.5 tbs light soy sauce, 1 tbs mirin, 1 tbs sake and 1/2 tsp sugar. Bring to a gentle simmer, taste and adjust seasoning so the broth is light and slightly savory, not salty. Remove from heat and keep warm.

Preheat your broiler (grill) to high (or oven to 240°C / 465°F if broiler not available). Butter a 20 x 20 cm (or similarly sized) ovenproof shallow gratin dish or 4 individual ramekins with 1 tbs butter total.

Prepare mochi: if using packaged mochi blocks, cut them into bite-size pieces (about 2–3 cm). To soften, briefly microwave the pieces in a covered heatproof bowl for 30–45 seconds until pliable but not fully melted, or warm them 1–2 minutes in a lightly oiled nonstick pan until beginning to puff. Arrange mochi pieces evenly in the buttered gratin dish(s).

Pour the warm light soy-dashi broth into the dish so it comes up about halfway around the mochi pieces (use all or most of the 400 ml depending on dish depth) — the mochi should be partially submerged but not floating free. This creates a light braising liquid that will keep the gratin saucy.

Prepare the mentaiko: using kitchen scissors or a small knife, split each sac and gently scrape or squeeze the roe into a small bowl, discarding the membrane pieces.

Add 3 tbs mayonnaise and 1/2 tbs sake to the mentaiko. Mix gently until combined into a smooth, spreadable paste. If you like a brighter note, stir in 1/2 tsp lemon juice. Taste and adjust (more mayo for milder, more mentaiko for stronger spice).

Spoon dollops of the mentai-mayo mixture evenly over the mochi pieces so each piece gets some roe topping.

Evenly scatter shredded mozzarella over the mentai and exposed mochi, covering most of the surface. The cheese should form a blanket over the gratin.

Place the gratin dish on a baking sheet (to catch any bubbling) and bake under the preheated broiler/grill for 3–6 minutes, watching closely, until the cheese is bubbling and has golden spots. If using an oven at 240°C, bake for 8–12 minutes until cheese is melted and slightly browned. The broth should be gently simmering at the edges — do not overbake or the mochi will become overly chewy.

Remove the gratin from the oven. Sprinkle sliced green onions evenly over the hot cheese so they soften slightly but remain bright.

Finish with a light scattering of kizami nori across the top and a pinch of shichimi togarashi if using for a spicy, aromatic kick.

Let the gratin rest 1–2 minutes (the cheese will be very hot). Serve immediately, scooping mochi, cheese, and some broth into each bowl so diners can enjoy the light soy-dashi with the cheesy mentai mochi.