Preheat your oven to 400 degrees F. Line a 12-cup muffin tin with paper liners or grease well.
In a large bowl, whisk together the flour, 3/4 cup sugar, baking powder, and salt.
In a separate bowl, whisk the melted butter, 2 eggs, milk, and 1 teaspoon vanilla extract until combined.
Pour the wet ingredients into the dry ingredients. Mix gently until just combined; do not overmix. Fold in the blueberries carefully.
Prepare the cream cheese filling: In a small bowl, beat the softened cream cheese, 2 tablespoons sugar, egg yolk, and 1/2 teaspoon vanilla extract until smooth.
Fill each muffin cup about halfway with the batter. Drop a spoonful (about 1 teaspoon) of the cream cheese mixture into the center of the batter in each cup. Top with remaining batter, filling cups about three-quarters full.
Bake for 18 to 20 minutes, or until a toothpick inserted into the muffin part comes out clean.
Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.
Notes
If you use frozen blueberries, do not thaw them first; toss them with one teaspoon of flour before adding them to the batter to prevent sinking.
For a cream cheese swirl effect, use a knife or skewer to gently swirl the cream cheese layer into the batter once in the muffin cup.
Store leftover muffins in an airtight container at room temperature for up to 3 days.