Preheat your oven to 350°F (175°C). Line a muffin tin with cupcake liners or grease it lightly.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set this aside.

In a large mixing bowl, cream the softened butter and granulated sugar using an electric mixer until the mixture is light and fluffy.

Beat in the eggs, one at a time, followed by the milk, lemon zest, and lemon juice. Make sure the mixture is well combined.

Gradually add the dry ingredient mix to the wet mixture. Stir gently until no streaks of flour remain. Finally, fold in the poppy seeds.

Spoon the batter into the prepared cupcake liners, filling each about two-thirds full.

Bake for about 15-20 minutes or until the tops are golden and a toothpick inserted in the center comes out clean.

Remove the cupcakes from the oven and let them cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.

In a mixing bowl, combine the blackberry puree with softened butter. Gradually add powdered sugar, beating until the frosting is smooth and creamy.

Once cooled, frost the cupcakes generously with the blackberry frosting.

Present your Lemon Poppy Seed Cupcakes with Blackberry Frosting at your next family gathering and watch them disappear!