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

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

In another bowl, combine the melted butter, milk, eggs, and vanilla extract.

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

In a small bowl, mix together the flour, brown sugar, and cinnamon.

Add the cold cubed butter and use a fork or pastry cutter 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 the muffin batter.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted in the center comes out clean.

Allow to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.