Preheat the oven to 375°F (190°C) and line a muffin tin with paper liners.

In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.

In another bowl, mix the buttermilk, melted butter, eggs, and vanilla extract until well combined.

Pour the wet ingredients into the dry ingredients and stir until just combined. Gently fold in the blueberries.

In a small bowl, combine the flour, brown sugar, cold butter, and cinnamon. Use a fork or your fingers to mix until crumbly.

Scoop the muffin batter into the prepared muffin tin, filling each cup about 2/3 full.

Sprinkle the streusel topping evenly over each muffin.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.

Let the muffins cool in the tin for 5 minutes, then transfer to a cooling rack.