Activate the Yeast: In a bowl, combine the warm milk with the dry yeast, sugar, and vanilla sugar. Mix with a whisk to combine well. Allow it to sit for about 10 minutes until bubbly.
Mix Wet Ingredients: Add the egg and melted butter to the yeast mixture, stirring well to combine.
Incorporate Flour: Gradually stir in the flour, mixing until a rough dough forms.
Knead the Dough: Knead the mixture on a floured surface for about 5-10 minutes, adding more flour as necessary until you achieve a soft, non-sticky dough.
Let it Rise: Place the dough in a greased bowl and cover with a cloth. Allow it to rise in a warm spot for about 1 hour or until it doubles in size.
Divide the Dough: Once risen, punch down the dough and place it on a floured surface. Cut it into 12 equal sections.
Shape the Croissants: Roll each section into a flat rectangle. Spread a tablespoon of chocolate cream on the bottom of the rectangle, fold the edges over, and roll tightly from bottom to top.
Prepare for Baking: Place each rolled croissant on a parchment-lined baking tray. Brush the tops with beaten egg, cover, and let them rest for another 10-15 minutes.
Bake: Preheat your oven to 375°F (190°C) and bake the croissants for about 20 minutes or until golden brown.
Finish and Serve: Remove from the oven, brush with melted butter, and dust with powdered sugar before serving. Enjoy warm!