- Heat oven to 200 degC. Grease a 12-hole large (Texas) muffin pan.
- Prepare the muffin topping by combining melted butter with cocoa and brown sugar.
- Make the muffin mixture. Place butter and sugar in a bowl and beat until pale and creamy.
- Beat in the eggs, one at a time, then beat in the yoghurt and coffee mixture.
- Gently stir in the sifted flour, stirring just enough to combine into a smooth mixture.
- Stir in chocolate. Spoon mixture into prepared tins. Spoon over prepared topping and swirl this into each muffin with a skewer.
- Bake for 25 to 30 minutes or until a skewer inserted in the centre of one muffin comes out clean.