Line a slice pan with baking paper and set aside.

In a large saucepan melt the butter then add sugar, cocoa and milk. Whisk together and bring to the boil. Boil for one minute. Remove from heat.

Add the Nutella, vanilla, rolled oats and rice bubbles to the pan and combine well.

Pour into slice pan and smooth flat with the back of a metal spoon. Scatter over your choice of sprinkles.

Refrigerate until set. This will take about 3 hours. Cut into squares with a sharp knife