Place the mascarpone, heavy cream, mixing bowl, and whisk attachments in the refrigerator for 30 minutes to chill thoroughly.

Preheat the oven to 180°C / 350°F and line the baking tray with parchment paper.

Melt the 200 g dark chocolate with the 60 g butter in a saucepan over low heat.

Remove the saucepan from the heat and let the chocolate-butter mixture cool for 5 minutes.

Whisk the 2 eggs with the 90 g white sugar and 45 g brown sugar until the mixture is smooth and slightly lighter.

Pour the cooled chocolate-butter mixture into the egg mixture and whisk until evenly combined.

Add the 90 g wheat flour and 5.5 g baking powder to the bowl.

Fold the dry ingredients into the batter with a rubber spatula just until no dry flour remains.

Fold the 100 g chocolate chips and 1 g fleur de sel into the brownie cookie dough.

Scoop 6 equal portions of dough onto the lined baking tray, leaving space between each portion.

Bake for 10 to 12 minutes, until the edges are set but the centers remain soft.

Remove the cookie brownies from the oven and let them cool on the baking tray until room temperature.

Pour the chilled 100 ml heavy cream and 150 g mascarpone into the chilled mixing bowl.

Add the 15 g powdered sugar and 5 ml vanilla extract to the cream mixture.

Whip the mixture with an electric hand mixer until stiff peaks form.

Transfer the mascarpone whipped cream to a piping bag fitted with a piping tip.

Pipe the mascarpone whipped cream over the cooled cookie brownies and serve immediately.