For the ham croissants, cut the ham into small cubes. Finely chop the parsley. Mix ham, parsley and sour cream and season to taste with salt and pepper.
Preheat oven to 180 degrees hot air. Roll up the puff pastry, portion into small squares and place a small amount of filling in the center of each square.
Then roll into croissants. Simply roll the top left corner down to the right. Then bend into croissant shape. Twist the ends together again to prevent the filling from squeezing out.
Place the ham croissants on a baking tray lined with baking paper, brush with beaten egg yolk and bake for about 20 minutes.