step 1
Preheat the oven to 180°C/350°F, Gas Mark 4 or 160°C for a fan assisted oven.
step 2
In a large bowl, beat the butter, 180g caster sugar / 3 tbsp of Stevia sweetener and the vanilla extract together until the mixture is light and fluffy. Beat in the eggs, one at a time, then sift the flour, and baking powder if using plain flour, over the mixture and fold in with 2 tbsp of the milk.
step 3
Separate 1/3 of the mixture into another bowl. Add the coco powder to that bowl and stir together until well mixed. Alternating the chocolate mixture with the vanilla mixture, put four half-teaspoons of both into each paper muffin case. Take a the back of a teaspoon and stir the vanilla and chocolate mixtures together so that they create a swirling pattern
step 4
Bake for 25 minutes or until well risen and springy to the touch. Transfer to a wire rack to cool.