For base

Oven preheated to 180C and a rectangular slice tin (20x30cm) oiled and lined with baking paper.

Place butter, sugar into a heat proof bowl and heat in microwave for 1 min, stir and heat again for additional min. Stir mixture until it comes together (usually 1 min or 2), place to one side to cool slightly.

Sift cocoa powder and besan flour together in a separate bowl. Gradually stir butter mixture into dry mix until combined. Add eggs and stir until fully incorporated.

Poor into the prepared tin and bake for 25 mins. The brownies will look a little undercooked in the middle when done. Leave in tin to cool.

Then cover and place in refrigerator until fully chilled for mousse layer.

Mousse:

Melt the chocolate in a large heatproof bowl set over a saucepan of gently simmering water. Leave to cool until just warm.

Using an electric stand mixer, whisk the eggs and yolks together until thick and pale.

In a separate bowl, whip 300ml of the cream to soft peaks.

Heat the remaining cream in a small saucepan over low heat until simmering, remove the pan from the heat.

Soak the gelatine in a sauce of cold water until soft then squeeze out any excess liquid. Stir the soaked gelatine into the cream until dissolved.

Fold the egg mixture into the melted chocolate until combined, then add the warm cream.

Finally, fold through the whipped cream.

Pour mousse onto prepped brownie and place in the fridge to set overnight.

Dust the top of the mousse with a good layer of cocoa powder and cut using a clean hot knife. Keep in an airtight container in the fridge for up to 5 days.