Preheat the oven to 400 F (200 C).
Prepare a baking sheet by lining it with parchment paper. Set aside.
On a floured work surface, roll out the puff pastry into a circle that is 1/8 inch (3 mm) thick.
Using a spatula, spread the goat cheese over the pastry.
Arrange the prosciutto slices on top and use a rolling pin to press the ingredients onto the pastry.
Using a pizza cutter, cut the preparation into 16 triangular parts.
Starting from the widest part, roll the parts to give them a crescent shape.
Beat the egg yolk and milk together.
Dip the mini-croissants into the mixture and place them on the reserved baking sheet.
Bake for 20 to 25 minutes, or until the pastry is golden brown.
Serve warm.