Lemon Poppy Seed Cupcakes

• 1 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/4 teaspoon salt
• 1/2 cup unsalted butter, softened to room temperature
• 1 cup white sugar
• 2 tablespoons lemon zest*
• 2 large eggs
• 1 teaspoon vanilla extract, room temperature
• 2/3 cup sour cream, room temperature
• 3 tablespoons lemon juice*, freshly squeezed
• 1 1/2 tablespoons poppy seeds

Blackberry Frosting*

• 1 1/2 cups blackberries, fresh or frozen
• 1 cup unsalted butter, softened to room temperature
• 4 cups powdered sugar
• 1/4 teaspoon salt
• 1 tablespoon cream or cream, if needed