We start with the cookie:

1. In a bowl, mix the flour, baking soda, vanilla, and salt.
2. In another bowl or in a mixer, add the butter and both types of sugar. Beat until the mixture becomes fluffy, then add the egg. Gradually add the flour mixture and continue mixing until smooth and fluffy. Finally, add the chopped chocolate and mix well. Place the mixture in the fridge while preparing the brownie.

For the brownie:

1. Melt the butter and chocolate using a bain-marie. Fill a saucepan halfway with water and bring it to a boil. Place a heatproof glass bowl on top, ensuring it does not touch the water. Let the butter-chocolate mixture melt, stirring until smooth. Remove from heat and allow it to cool slightly.
2. Alternatively, cover the bowl with plastic wrap and microwave for 1½–2 minutes. Remove, stir, and set aside.
3. In a bowl, mix the flour, cocoa, and salt.
4. In another bowl or mixer, beat the eggs and sugar until fluffy. Add the vanilla extract and cognac. Pour in the melted butter-chocolate mixture, then gradually add the flour mixture. Mix well.
5. Grease and dust with cocoa a 22cm round Bugatti tart pan with silicone coating. Pour in the brownie mixture. Using an ice cream scoop, place portions of the cookie dough over the surface of the brownie. Alternatively, shape the dough into small balls and place them on top.
6. Bake in a preheated oven at 180°C for 25 minutes.
7. Serve warm, but it is also delicious at room temperature.