Preheat the oven to 190 °C/170 °C fan/gas mark 5 and line a 12 hole muffin tin with paper muffin cases.

Stir the flour, baking powder and sugar together in a bowl. Chop 110 g of the chocolate in to small chunks and add to the dry ingredients. Make a well in the centre.

In a bowl, beat the egg with the milk and oil. Pour all at once into the well in the flour mixture. Mix quickly and lightly with a fork but do not beat. Gently stir in the OREO Cookie Pieces.

Divide the batter between the 12 muffin cases. Immediately bake for about 25 minutes or until well risen and golden. Leave to cool.

When the muffins have cooled, pop the remaining 30 g of white chocolate into a disposable piping bag and melt in the microwave on a low setting. Casually pipe the white chocolate over the muffins and leave to set. Best eaten on day of baking.