Make the cheesecake mixture: In a small bowl, beat the softened cream cheese with 3 tablespoons sugar, 1 teaspoon vanilla, sour cream, and cornstarch until smooth. Set aside.

Combine dry ingredients: In a large bowl, whisk flour, 3/4 cup sugar, baking powder, baking soda, and salt.

Mix wet ingredients: In a separate bowl, whisk melted butter, buttermilk, eggs, remaining 1 teaspoon vanilla, and lemon zest until well combined.

Bring the batter together: Pour wet into dry. Stir gently with a spatula until just combined. It’s okay if a few streaks of flour remain—don’t overmix.

Fold in blueberries: Toss blueberries in a teaspoon of flour if they’re extra juicy, then fold them into the batter with a few gentle strokes.

Fill the cups: Spoon about 2 tablespoons of muffin batter into each liner. Add 1 heaping tablespoon of the cheesecake mixture on top. Cover with another tablespoon or two of batter until cups are about 3/4 full.

Create the swirl: Use a toothpick or skewer to gently swirl the cheesecake layer into the muffin batter. Don’t overdo it—2–3 light figure-eights are enough.

Top and bake: Sprinkle with turbinado sugar if using. Bake for 18–22 minutes, or until the tops are set and a toothpick inserted near the edge comes out clean (a little cheesecake on the pick is fine).

Cool properly: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. Cool at least 20 minutes before eating so the cheesecake layer sets.