Lemon-Blueberry Cupcakes with Blueberry-Lemon Buttercream Frosting

**Make the Blueberry Jam:** Combine 1 1/2 cups frozen blueberries, 2 tablespoons granulated sugar, and 1 teaspoon lemon juice in a small saucepan over medium heat. Bring to a simmer and cook, stirring occasionally, until the mixture has reduced and thickened, about 12 minutes.

Pour the blueberry mixture through a fine-mesh sieve, pressing on the solids to extract as much jam as possible (you should have approximately 1/4 cup). Discard the solids and refrigerate the jam until completely cool, at least 30 minutes.

**Prepare the Cupcakes:** Preheat oven to 350°F (175°C). Line 18 muffin cups with paper liners.

In a medium bowl, whisk together 1 3/4 cups all-purpose flour, 2 teaspoons baking powder, and 1/2 teaspoon salt.

In a large bowl, cream together 1 cup granulated sugar and 1/2 cup softened butter until light and fluffy. Beat in the eggs one at a time, mixing well after each addition. Stir in 3 tablespoons lemon juice, 1 1/2 tablespoons lemon zest, and 1/2 teaspoon vanilla extract until combined. Gradually add the dry ingredients in two additions, alternating with the buttermilk, beating until just combined after each addition (the batter will be somewhat thick).

In a separate small bowl, toss the remaining 1 1/2 cups frozen blueberries with 1 tablespoon all-purpose flour. Gently fold the floured blueberries into the cupcake batter. Spoon the batter into the prepared muffin cups, filling each about 3/4 full.

Bake for 20 minutes. Check doneness by inserting a toothpick into the center of a cupcake; if it comes out clean, they are done. If not, continue baking for 4-8 more minutes. Let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely, about 20 minutes.

**Make the Blueberry-Lemon Buttercream Frosting:** While the cupcakes are cooling, remove the blueberry jam from the refrigerator. Measure out 1/4 cup for the frosting and reserve any extra for another use.

In a large bowl, beat 1 cup softened butter until creamy and smooth. Gradually add 1 cup powdered sugar, 2 teaspoons lemon zest, 1 1/2 teaspoons lemon juice, and 1/8 teaspoon salt; beat until thoroughly combined. Mix in the 1/4 cup blueberry jam until combined. Add the remaining 2 1/2 cups powdered sugar in two additions, beating until smooth after each addition. Add 1 tablespoon heavy cream and beat until the frosting is smooth and fluffy, 1-2 minutes more.

**Frost the Cupcakes:** Once the cupcakes are completely cooled, frost generously with the blueberry-lemon buttercream.