Preheat the oven to 180 degrees C. Grease a cake tin.
Melt the chocolate in a double boiler over medium heat. Meanwhile, separate the egg whites from the yolks. Whisk the sugar with the egg yolks until foamy in a bowl. Whisk the egg whites until stiff in another bowl.
Remove the melted chocolate from the double boiler and add the butter. Stir until melted. Stir in the strawberry sauce, flour and then the mint in the chocolate mixture.
Gently stir in the egg whites into the chocolate mixture, lift the batter while stirring to keep the batter smooth.
Add the batter to the prepared cake tin and bake in the oven for 45 minutes.
Remove from the oven, turn the cake out of the cake tin and place it on a rack. Decorate the cake as desired.