Rub soft butter with fingers into the sifted flour. Pour yeast into a cup with warm milk, add a pinch of sugar. Mix, cover with a cloth and set aside for 15 minutes to rise.
Beat egg with powdered sugar, add it to the flour with butter. Pour in the yeast and vanilla extract. Knead the dough for about 10 minutes until it is smooth and does not stick to your hands. Transfer to a bowl, cover with plastic and refrigerate for 2 hours.
Preheat the oven to 200°C. Form 3 balls from the dough. Roll out into 3 cakes, dusting lightly with flour. Cut each cake into 8 'triangles' the way you cut pizza. On each triangle, at its wider part, place 1 teaspoon of jam or 1 cherry or 1 tablespoon of roasted apples, or 1 piece of chocolate or 1 teaspoon of Nutella. Roll from the wider end forming croissants.
Arrange on a baking sheet lined with parchment paper. Bake for about 15 minutes or until lightly golden. Dust with powdered sugar.
