Spray a square baking tin, measuring approx. 23cm x 23cm (9 x 9 inch) with low fat cooking spray. Melt the low fat spread in a saucepan. Remove from the heat and stir in half the white chocolate.

For decades, Ritter Sport has marketed its chocolate bars on their unique, square shape. So when rival brand Milka challenged its German monopoly on square chocolate, the battle lines were drawn.

Melt the chocolate with the butter and zest over a ... Chill it in the fridge again and then cut it to whatever size squares you would like. Line a 9inch square cake tin and heat the oven to ...