Preheat oven to 220°C/430F/Gas Mark 7. Line a 12 cup muffin pan with cupcake liners.
Roughly chop the chocolate and keep aside 2-3 large chunks per muffin, about 36 chunks. Set aside.
125 grams caramelised white chocolate, 125 grams milk chocolate
In a large bowl, sift together the flour, cocoa powder, and baking powder. Add in the salt and sugar. Whisk through to combine. Add the chocolate chunks and stir through the flour mixture.
300 grams plain flour, 45 grams unsweetened cocoa powder, 150 grams white granulated sugar, ½ teaspoons table salt, 3 teaspoons baking powder
In a separate mixing bowl, jug or saucepan, melt the butter and allow it to cool. Add in the rest of the wet ingredients and whisk together until well combined.
125 grams butter, 2 eggs, 125 grams Greek yogurt, 125 grams milk, 3 teaspoons vanilla extract
Pour the wet ingredients into the dry ingredients and mix until just combined.
Divide the muffin batter evenly between the 12 cupcake liners. Filling the liners to the top. Top the muffins with the extra chocolate chunks.
Bake at 220°C/430F/Gas Mark 7 for 5 minutes. Turn down the oven to 200°/390F/Gas Mark 6 and bake for a further 12 to 15 minutes (check at the 12-minute mark and removed when just baked).
Allow the muffins to cool for 10 to 15 minutes before serving.