Heat oven to 180℃/160℃ fan/gas 4. Melt the dark chocolate and butter in a heatproof bowl over a pan of simmering water and stir until smooth, remove from the heat and leave to cool.
Whisk the eggs and Tate and Lyle Golden Caster Sugar in a large bowl with an electric mixer until thick and creamy.
Pour the cooled chocolate mix into the bowl and gently fold in.
Next fold in the sifted flour and cocoa until the mixture looks fudgy.
Stir in the white and milk chocolate pieces and pour the batter into a greased and lined 20cm square tin.
Bake the brownies for 25 minutes until the top looks shiny and crusty. Cool in the tin and then lift out in one piece and cut into triangles.
Decorate with pretzels, googly eyes and red smarties for Rudolph faces and use icing pens and sprinkles to make colourful Christmas trees.
These chocolate brownies will keep for up to two weeks in an airtight tin or frozen for a month.