Chocolate Mango Cake

Preheat oven to 350 degrees F / 180 C. Line an 8 inch round baking dish with parchment paper and set aside.
Whisk together the sour cream, oil, eggs and vanilla extract and set aside.
In a separate mixing bowl whisk the brown sugar, salt, baking powder and soda, cocoa powder and flour until well combined.
Pour the wet ingredients into the dry ingredients and mix until combined.
In a separate bowl mix the boiling water and instant coffee.
Stir the coffee mixture into the cake batter and mix until incorporated.
Pour the cake batter into the prepared tin and bake for 45-50 minutes or until an inserted skewer comes out clean. If the cake is starting to brown before it is cooked cover it with foil to prevent it from burning.
Allow to cool in the cake baking dish for 10 minutes before removing and cooling completely on a cooling rack.
While the cake is cooling prepare the buttercream filling: Whip the pasteurized egg whites with the powdered sugar for 3 minutes. Add half the butter, whip until smooth. Add remaining butter and mango extract, whip for 4-5 minutes. Adjust the flavor to suit by adding an additional tsp of mango extract if desired.
Add a drop of orange food coloring and mix thoroughly if using.
Slice the cake in half with a serrated knife.
Spread ½ of the buttercream, in an even layer, over the cake base. Add the top layer of cake, finish off with remaining buttercream and sliced mango if using.
Chill for 1 hour before serving.