1. Preheat the oven to 350°F. Line a muffin tin with paper. Melt the butter in a small pan or in the microwave, then leave to cool.
2. Put the flour, sugar, baking powder and baking soda in a freestanding mixer with a paddle attachment (or use a bowl and a handheld mixer) and beat on low speed.
3. Put the buttermilk, egg and vanilla extract into a bowl and mix to combine. Slowly pour into the flour mixture and continue to beat until just combined.
4. Pour in the cooled melted butter and beat until the butter has just been incorporated, then turn the mixer up to medium speed and beat until the mixture is smooth.
5. Gently fold in the blueberries until evenly dispersed. Divide the muffin mixture among the paper,, filling each one two-thirds full and bake for 20 minutes or until golden brown and the muffin bounces back when touched. A toothpickr inserted in the middle should come out clean.
6. Leave muffins to cool slightly in the tin before turning out on to a wire rack to cool completely.
7. To serve, arrange the muffins on a plate in a pyramid, if desired or wrap in greaseproof paper to take on picnics or in packed lunches.