In a heatproof bowl, combine the butter and chocolate and melt them together over a hot water bath or in the microwave, a few seconds at a time.
While the chocolate is melting, mix the eggs and 100g of sugar until triple in volume then stir in the vanilla extract.
With the mixer on low speed, incorporate the chocolate into the egg mixture.
Add the flour and mix just until well incorporated.
Cover the batter with plastic wrap and refrigerate at least 2 hours, preferably overnight.
The next day, line 2 baking sheets with baking paper. Take the bowl out of the fridge and take small spoonfuls of dough. Roll the dough between the palm of your hands to form a ball then roll the ball through grnulated sugar first, followed by powdered sugar.
Carefully place the coated cookies on a prepared baking sheet.
Bake in the preheated oven at 180C for 8-10 minutes, not more as they need to remain soft on the inside.
Repeat with the remaining dough and only make one pan at a time as the dough needs to stay in the fridge as one batch bakes.
Let them cool in the pan then transfer them on a platter.
Use good quality dark chocolate of at least 70% cocoa content, otherwise the batter won't have the desired consistency and the cookies won't rise or bake as they should. Plus, it also affects the taste.
Recipe by Pastry Workshop at http://pastry-workshop.com/chocolate-crinkles-fursecuri-cu-ciocolata/