Put almonds, butter, and sugar in a blender and mix until you obtain a homogeneous and soft mixture.
Roll out the pastry sheet and cut it into squares of 6 cm each.
Put a teaspoon of almond cream in each square.
Fold the edges by wetting them with a little water.
Brush the almond pastries with a mixture of egg yolk and milk.
Add some almond flakes and bake at 180°C (356°F) for about 15-20 minutes until browning.
Let them cool down and sprinkle with powdered sugar.