Preheat the oven to gas 4, 180°C, fan 160°C. Grease and line the base and sides of a 25cm x 16cm brownie tin.

In a mixing bowl, beat the butter and sugars with an electric whisk, until light and fluffy. Add the vanilla, then beat in the eggs, one at a time. Fold in the chocolate, followed by the flour and cocoa. Pour into the prepared tin and bake for 25-30 mins, or until set but soft in the centre. Cool in the tin.

Meanwhile, make the glaze. In a large bowl, mix the melted chocolate with the butter and icing sugar, until glossy.

Turn out the brownie on to a board and peel off the baking paper. Pour over the glaze, letting it run over the sides. Starting in one corner, scatter over the hundreds and thousands to create a graduated effect. Cut into squares.