Step 1: Preheat and Prepare

1. Preheat your oven to 375°F (190°C).
2. Line a 12-cup muffin tin with paper liners or grease the cups lightly.

Step 2: Make the Crumb Topping

1. In a small bowl, mix together the flour, granulated sugar, brown sugar, and cinnamon.
2. Stir in the melted butter until the mixture becomes crumbly.
3. Set aside for later.

Step 3: Prepare the Muffin Batter

1. In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
2. In another bowl, whisk the melted butter, sugar, eggs, buttermilk, and vanilla extract until smooth.
3. Gradually mix the wet ingredients into the dry ingredients, stirring gently until just combined. (Don’t overmix—it’s okay if the batter is a little lumpy!)

Step 4: Add the Blueberries

1. Toss the blueberries with 1 tablespoon of flour to prevent them from sinking in the batter.
2. Gently fold the blueberries into the muffin batter.

Step 5: Fill the Muffin Cups

1. Divide the batter evenly among the muffin cups, filling them about ¾ full.
2. Sprinkle the crumb topping generously over each muffin.

Step 6: Bake!

1. Bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean.
2. Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.