Add the chopped blackberries and gently fold them into the cake batter– try not to overmix the batter! Mix just until the berries are incorporated.
½ cup finely chopped blackberries
Divide the cake batter between the muffin tins, filling each one with about ¼ cup of batter.
Bake for 15-17 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cupcakes to a wire rack and cool completely before frosting.
For the Blackberry Buttercream
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed until lightened, about 30 seconds.
½ cup unsalted butter
With the mixer on low speed, slowly add the powdered sugar.
2¼ cups powdered sugar
Once all of the powdered sugar has been incorporated, add the blackberry jam and vanilla extract.
¼ cup blackberry jam or preserves, 1 teaspoon pure vanilla extract
Turn the mixer to medium-high speed and beat until the frosting is light and fluffy, about 1-2 minutes.
Transfer the buttercream to a piping bag and frost the cooled cupcakes as desired.
Notes
Make sure to spoon and level your ingredients into the measuring cup for the most accurate results.
Generously spray your cupcake tin or line it with paper liners for easy release.
Don’t overmix the cupcake batter, or you could end up with dry, dense cupcakes. Only mix until there are no lumps in the batter.
Don't overfill the wells of the cupcake tin or you will end up with "muffin tops" on your cupcakes, and they will be more difficult to frost.
Allow the cupcakes to cool completely before frosting; otherwise, the frosting will melt off.
Storage: Store blackberry cupcakes in an airtight container in the refrigerator for up to 2 days. Freeze cupcakes and buttercream separately for up to 3 months.