Preheat your oven to 190°C and grease a non-stick muffin tray. Melt your butter in a small pan over a medium heat until it starts to foam and froth. Once the butter starts to separate into creamy solids and golden yellow liquid, wait for the solids to turn a golden brown and then remove from the heat. Leave to cool to room temperature.

Mix all the remaining ingredients, apart from the blueberries, chocolate chips and icing sugar, using an electric hand whisk until fluffy. Add the melted butter, mix again, and stir through the chocolate chips and blueberries by hand at the end, to keep the berries whole. Let the batter rest for 30 minutes in the fridge, to get rid of any bubbles.

Fill the greased moulds three-quarters full. Place in the oven and bake for 15-20 minutes, until cooked through and springy. Leave them to cool in their moulds for 10 minutes, before transferring to a wire rack to cool completely. Dust with icing sugar to serve. They will keep for up to three days in an airtight container.