Preheat the oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together the all-purpose flour, 3/4 cup granulated sugar, baking powder, baking soda, and salt.
In a separate medium bowl, whisk together the melted butter, buttermilk, eggs, and 1 teaspoon vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and gently fold together until just combined. Do not overmix.
Fold in the fresh blueberries carefully to avoid breaking them.
In a small bowl, beat the softened cream cheese with 1/4 cup granulated sugar and 1 teaspoon vanilla extract until smooth and creamy.
Fill each muffin cup about halfway with the blueberry batter.
Add about 1 tablespoon of the cream cheese mixture into the center of each muffin cup.
Top with the remaining blueberry batter until each cup is about 3/4 full, covering the cream cheese filling.
Bake in the preheated oven for 22 to 25 minutes, or until a toothpick inserted into the muffin (avoiding the cream cheese center) comes out clean.
Remove the muffins from the oven and allow them to cool in the tin for 5 minutes.
Transfer the muffins to a wire rack to cool completely before serving.