Whip the egg white until frothy.
Take small pieces of dough (1round 15g each) and roll them into a ball.
Roll each ball into the whipped egg white then through the chopped hazelnuts.
Place the cookies on a baking sheet lined with parchment paper. Using your fingertip, make a small indentation in the center of each cookie.
Bake in the preheated oven at 350F - 180C for 15 minutes or until the edges turn slightly golden brown and crisp.
Remove the cookies from the oven and let them cool in the pan then fill the indentations you made earlier with melted chocolate.
Let the chocolate set before serving.