Instructions

• Preheat oven to 375°F. Line a 24-cup mini muffin pan or a 12-cup regular muffin pan with paper liners.
• Measure the flour: measure out the full amount (1 1/2 cups + 1 tablespoon). Remove and set aside 1 tablespoon of the measured flour to toss with the blueberries; you will use the remaining 1 1/2 cups in the batter.
• In a large bowl, beat 1 stick (8 tablespoons) salted butter (room temperature) with 1/2 cup granulated sugar and 1 tablespoon lemon zest until combined and slightly lightened.
• Add 1/2 cup plain Greek yogurt and 1 tablespoon vanilla extract to the butter mixture and beat until smooth.
• Add the 3 eggs, one at a time, beating until each is incorporated before adding the next.
• In a separate bowl, whisk together the remaining 1 1/2 cups flour, 2 teaspoons baking powder, and 1/2 teaspoon salt. Add the dry ingredients to the wet ingredients and mix just until combined — do not overmix.
• Toss 1 cup blueberries with the reserved 1 tablespoon flour to coat, then gently fold the blueberries into the batter.
• Add 3 tablespoons blueberry jam to the batter in spoonfuls and use a few gentle swirls with a knife or spatula to create a marbled effect; do not overmix.
• Divide the batter evenly among the prepared muffin cups, filling each most of the way full.
• (Optional) To make the cinnamon-sugar topping: stir together 1/2 cup granulated sugar and 2 teaspoons cinnamon in a small bowl. Brush the tops of the filled muffins lightly with 2 tablespoons melted butter, then sprinkle the cinnamon-sugar evenly over the muffin tops.
• Bake mini muffins 18–22 minutes or regular muffins 28–32 minutes, until the tops are set and a toothpick inserted in the center comes out with a few moist crumbs (muffins should not be wet).
• Let muffins cool in the pan for about 5 minutes, then transfer to a wire rack to cool completely.