A common baking recipe for a Mandelfisch:

Ingredients for the dough:
1 pinch of blowing salt, e.g. baking soda
1 table spoon of milk, used to solve the blowing salt in
240g flour (wheat)
100g sugar
80g butter (from cow milk)

Solve the blowing salt in the milk, mix all ingredients and make a dough. Let dough rest for a few hours (presumably at room temperatures). Butter the form, use 2/3 of the dough for the bottom and sides, the rest as a cover. The filled fish is typically about two inches high. Usually the recipes say to use a fish form, but of course any baking form will do, the resulting cake usually is 4-5cm (2inches, perhaps a bit less) high.

The fillings:
100g sugar
130g ground almonds
50g ground walnut
1 tea spoon lemon juice
1 zest of one lemon
1 chicken egg
ground cinammon
milk

Mix everything (I'd whip the egg a bit beforehand), knead as necessary, and fill the form/fish. Cover the fish, bake for one hour at 180° celsius. Let the baked fish cool down, decorate with powdered sugar (dust sugar?).