• Preheat oven to 400 degrees F and line a 12 cup muffin tin with paper liners. Alternatively, you could spray the tin with non-stick spray or butter very generously and flour (like making a cake).

For the streusel:

• Combine streusel ingredients in a small bowl and pinch together until you have a cohesive, crumbly mixture. Set aside.

For the muffins:

• In a large bowl, combine flour, sugars, baking powder, and salt. Mix to combine and break up any brown sugar clumps.
• Melt butter either in microwave or on the stovetop and add to a bowl or large, spouted measuring cup. Whisk in milk, eggs, and vanilla until thoroughly combined.
• Pour this wet mixture into the dry ingredients and with a wooden spoon or rubber/silicone spatula mix until almost combined but a few streaks of flour remain.
• Add blueberries and gently fold in until combined and no more flour remains. Do not overmix, some lumps and bumps are good here and you don't want to break the berries.
• Divide batter evenly between 12 muffin tins.
• Divide streusel evenly on top of muffin batter and press down very gently to make sure it sticks.
• If desired, add a few blueberries to the tops of muffins and press down just slightly.
• Allow batter to sit for 20 minutes at room temperature before baking in preheated oven for 15-18 minutes.