Preheat oven to 400 degrees F. Line a 12-cup muffin tin with paper liners and set aside.

In a small bowl, beat the softened cream cheese, 3 tablespoons sugar, and 0.5 teaspoon vanilla until smooth and fluffy, about 1 minute. Transfer to a piping bag or zip-top bag with the corner snipped.

In a large bowl, whisk together the flour, baking powder, and salt until well combined.

In a separate bowl, whisk the melted butter and 0.75 cup sugar until combined. Add the eggs one at a time, whisking well after each. Stir in the milk and 1.5 teaspoons vanilla until smooth.

Pour the wet ingredients into the dry and fold with a rubber spatula until just combined - a few streaks of flour are okay. Gently fold in 1 cup blueberries, being careful not to overmix. The batter will be thick.

Spoon about 2 tablespoons batter into each muffin cup. Pipe a generous teaspoon of cream cheese filling into the center of each, then cover with remaining batter, filling cups nearly full. Press a few reserved blueberries on top. Use a toothpick to gently swirl the cream cheese up toward the surface in a figure-8 motion.

Bake for 20-22 minutes, until the tops are golden and spring back when lightly pressed, and a toothpick inserted into the muffin (not the cream cheese center) comes out clean. Cool in the pan for 5 minutes, then transfer to a wire rack.