Using an electric handheld mixer or stand mixer with paddle attachment, cream the butter and sugar together in a large bowl for about 2 minutes until light and fluffy.
1/2 cup (114g) unsalted butter, 1 cup (200g) granulated sugar
Add the eggs, lemon zest, and vanilla extract and mix until well combined.
2 large eggs, zest of 1 lemon, 1 tsp vanilla extract
With the mixer on low, add half of the flour mixture, followed by the buttermilk, then the remaining flour mixture. Mix until just combined after each addition.
1/2 cup (125ml) buttermilk
Gently fold in the blackberries using a rubber spatula. Evenly spoon the batter into the paper liners and top each muffin with sparkling sugar.
2 & 1/2 cups (2-6oz pints) blackberries
Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.
Notes
Leftovers can be stored in an airtight container for up to 3 days at room temperature or up to 5 days in the fridge.