Pre-heat oven to 350 degrees and line a cupcake tin with 12 papers.
In the bowl of a stand mixer or in a large bowl with a hand mixer, combine butter, confectioners’ sugar, and lemon zest. Beat the ingredients until combined and nice and fluffy.
Add the eggs to the batter in the mixer, one at a time, beating after each addition.
In a separate medium bowl, whisk together flour, baking powder, and salt. Set aside.
Beat in half of flour mixture. Add milk and lemon juice and beat to blend. Beat in remaining flour mixture and beat until just combined, taking care not to over-mix.
Pour the batter into cupcake papers in a cupcake tin, about ¾ to the top.
Bake at 350 degrees for 18-20 minutes, until a tester inserted into the cupcake comes out clean. Let cupcakes cool in the pan for a few minutes before moving to a rack to cool completely.
When cupcakes are completely cooled, core them either using a cupcake corer or a knife. Fill each cupcake with cooled lemon curd.
Frost cupcakes with blackberry cream cheese frosting and top each cupcake with a blackberry garnish.