In a small bowl, combine ½ cup of flour, ⅓ cup of brown sugar, 2 tablespoons of granulated sugar, ½ teaspoon of cinnamon, and ⅛ teaspoon of salt. Rub in the cold cubed butter until the mixture resembles coarse crumbs. Refrigerate while preparing the muffin batter.

Set your oven to 425°F (220°C). Line a 12-cup muffin pan with paper liners or generously grease the cups.

In a mixing bowl, whisk together 2 cups of flour, 2 teaspoons of baking powder, ½ teaspoon of baking soda, and ½ teaspoon of salt until combined.

In a large bowl, whisk together ½ cup of granulated sugar, ¼ cup of packed light brown sugar, 2 eggs, ½ cup of neutral oil, ½ cup of sour cream, ½ cup of buttermilk, 2 teaspoons of vanilla extract, and 1 teaspoon of lemon zest until smooth.

Gently add the dry mixture to the wet ingredients, folding just until a few streaks of flour remain.

Carefully fold in 1.5 cups of blueberries until evenly distributed.

Divide the batter evenly among the muffin cups, filling each nearly to the top.

Retrieve the streusel and evenly distribute it over each muffin, sprinkle coarse sugar on top if desired.

Bake at 425°F (220°C) for 5 minutes, then reduce temperature to 375°F (190°C) and bake for an additional 15-18 minutes until golden.

Allow muffins to cool in the pan for 8 minutes before transferring to a wire rack.