Preheat the oven to 180 Celsius / 356 Fahrenheit top and bottom heat. Grease the tin with nonstick cooking spray (or a little butter) and line the base with parchment paper, overlapping on the sides for easy removal.

Keep a third of the chocolate chips aside, melt the rest of the chocolate in a double boiler with the butter. Stir regularly until the mixture is completely melted and smooth. Allow to cool slightly.

In a large bowl, mix together the brown sugar, cocoa powder, salt and vanilla sugar.

Pour the melted chocolate butter mixture into the dry ingredients and mix well.

Add the eggs one at a time, whisking well after each addition.

Sift the cake flour over the chocolate mixture and fold in gently until well blended. Add the extra chocolate chips and mix again.

Pour the mixture into the tin and smooth down the top.

Bake the brownies for about 25-30 minutes, until a toothpick / skewer inserted in the center comes out almost clean.

Allow the brownies to cool completely in the tin before removing from the tin and cutting into squares. Enjoy!