Preheat your oven to 375 degrees and line a muffin tin with paper cups (or spray with non-stick spray).
In a medium bowl, whisk together the flour, sugar, baking powder, and salt. Set aside.
In a large bowl, whisk together the melted butter, eggs, milk, and vanilla.
Add the dry ingredients to the wet ingredients and stir until just combined. Do not overwork the batter.
Toss the blueberries with 1 tbsp of flour (this will keep the blueberries from sinking). Add the blueberries to the batter and gently stir. Divide the batter between 14-16 muffin cups.
In a medium bowl, combine all of the streusel topping ingredients. Using a fork (or your hand), until it’s crumbly in texture. Sprinkle some of the streusel over the muffins.
Bake in the over for 20-25 minutes until the muffins are fluffy and the streusel topping is golden. An inserted toothpick should come out clean.
Leave the muffins to sit in the hot muffin tin for a few minutes before removing to a cooling rack. Store in an air-tight container for up to 5-6 days. Enjoy!