Roughly 1 cup of blackberries (plus extra to garnish)
Preheat oven to 350 degrees F (175 degrees C).
Line 24 muffin cups with paper liners.
Cream sugar and 1/2 cup butter in the bowl of a stand mixer until fluffy. Beat in eggs, one at a time, and mix 1 1/2 teaspoons vanilla extract into mixture with the second egg.
Beat in flour and baking powder until thoroughly combined; beat in milk, lemon juice, and lemon zest to make a smooth batter.
Spoon the batter into the prepared muffin cups.
Bake in the preheated oven until cupcake edges are slightly golden brown and a toothpick inserted into the center of a cupcake comes out clean, 20 to 25 minutes. Cool cupcakes completely.
Frost and enjoy
In medium bowl, mix powdered sugar and butter with spoon or electric mixer on low speed. Stir in vanilla and 1 tablespoon of the milk.
Gradually beat in just enough remaining milk to make frosting smooth and spreadable. If frosting is too thick, beat in more milk, a few drops at a time. If frosting becomes too thin, beat in a small amount of powdered sugar.
Next, heat the blackberries in the microwave for about 15 seconds on high. Place them in a sieve and use a large spoon to press the juice through. Don't worry about the skin getting through, this is mainly to remove the seeds.
Beat the juice into the frosting and briefly chill.
Finally frost cupcakes, top with a blackberry and enjoy!
