Whisk together flour, baking powder, cardamom, and salt in a bowl.

In a separate bowl, cream together butter and sugar until light and fluffy.

Beat in egg yolk and milk until combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Divide the dough into two portions, one slightly larger than the other.

Form each portion into a disk, cover, and chill for at least 2 hours or overnight.

Butter a 9-inch tart pan.

Break the larger dough disk into pieces and press into the bottom and up the sides of the tart pan.

Smooth the surface and trim the edges.

Roll out the smaller dough disk and cut out decorative shapes.

Place the cutouts on a parchment-lined baking sheet and chill for 1 hour.

Preheat oven to 350°F (175°C).

Pulse almonds, powdered sugar, cardamom, and nutmeg in a food processor until finely ground.

Transfer the almond mixture to a bowl.

In a separate bowl, beat egg whites and vanilla until medium peaks form.

Gently fold the egg whites into the almond mixture.

Whisk egg yolk and water together for egg wash.

Fill the chilled tart crust with the almond filling, smooth the top.

Arrange the cutouts on top of the filling and brush with egg wash.

Bake for 30-35 minutes, or until the crust and cutouts are golden brown and the filling is set.

Let cool on a wire rack before serving.