Heavenly Chocolate Mint Slices — Prep time: 20 minutes. Cook time: 20 minutes (3 hours of chilling required). Serves: a party of people (approx 12 slices). Ingredients: The Base = 250g butter, at room temperature 1/2 cup brown sugar 1/4 cup caster sugar 1 egg 1 cup plain flour 1/3 cup dark cocoa 1/2 cup…