Line the base and sides of a 900g loaf tin with baking paper. Tip the condensed milk and chocolate into a wide nonstick pan and melt together on the lowest heat, stirring frequently.

Once melted, divide the mixture equally between 3 bowls. Add a different colouring to each bowl and stir in well. Pour into the tin in layers (you can swirl them together lightly, if you wish). Scatter over the marshmallows and sprinkles, lightly pressing them into the mixture. Cover and chill in the fridge overnight, or for at least 8 hours until set firm.

Tip the fudge out of the tin and remove the baking paper. Cut into slices, and then into fingers. Serve straight from the fridge.