Melt the dark chocolate and unsalted butter in the microwave for about 30 seconds.
Mix the egg, brown sugar, and salt, then add the melted chocolate and butter mixture.
Add the Nutella and vanilla extract and mix.
Sift the plain flour, baking powder, and baking soda, then mix into the batter.
Refrigerate the dough for 1 hour.
Cream the unsalted butter, sugar, and salt, then add the egg and vanilla extract.
Sift the cake flour and mix into the dough.
Refrigerate the dough for 1 hour.
Divide the dough into smaller pieces, about 7g each.
Divide the Nutella mixture into larger portions, about 10g each.
Flatten the dough and wrap the Nutella inside.
Shape the dough into round cookies and bake at 160°C (preheated to 170°C) for 12 minutes.
Let the baked cookies cool on a rack.
