Cut open the mentaiko and extract the roe.

Mix egg and yogurt in a bowl.

Add melted butter and pancake mix, mixing until no dry powder remains.

Place the dough on a surface and knead thoroughly.

Divide the dough into two portions, shape into balls, and roll into oval shapes.

Place melting cheese and mentaiko on the lower half of each oval dough, fold in half, and seal the edges.

Use chopsticks to create decorative patterns on the dough.