Melt 150 g of dark chocolate and 40 g of unsalted butter in the microwave for 30 seconds, then for another 30 seconds.
Whisk 1 egg and 55 g of brown sugar with 1 g of salt until combined.
Add the melted chocolate mixture and mix well.
Add 50 g of Nutella and 3 g of vanilla extract.
Sift in 60 g of all-purpose flour, 2 g of baking powder, and 1 g of baking soda, then mix well.
Chill the dough in the refrigerator for 1 hour.
Cream 75 g of unsalted butter with 55 g of sugar.
Add 25 g of egg and 2 g of vanilla extract.
Sift in 150 g of cake flour and 1 g of salt, then mix well.
Chill the dough in the refrigerator for 1 hour.
Divide the outer dough into 7 g portions.
Place 10 g of the Nutella brownie mixture in the center of each dough portion.
Cover the Nutella brownie mixture with the cookie dough.
Press the cookies onto a baking sheet.
Bake at 160 degrees Celsius for 12 minutes.
Let cool on a wire rack.
