Preheat oven to 400° F. Line a standard muffin tin with paper liners. Set aside.
Prepare the streusel. In a small bowl, use a fork to whisk the flour, brown sugar, sugar and cinnamon together. Add the melted butter and stir until clumps form. Place the bowl aside while preparing the muffin batter.
In a large bowl, whisk together 1 ¾ cup flour, baking powder and salt. Set aside.
In a medium bowl, combine sugar and melted butter. Whisk vigorously until butter is absorbed, about 1 minute. Add eggs and mix until combined. Add sour cream, milk and vanilla. Whisk again until all ingredients are thoroughly incorporated.
Pour wet ingredients over dry ingredients. Stir just until combined making sure to scrape the bottom of the bowl. Toss diced strawberries with 2 Tablespoons flour until coated, then gently fold the strawberries into the muffin batter (avoid overmixing).
Scoop batter into prepared muffin tin (I like to use an ice cream scoop for this). Fill until about 3/4 quarters full. Batter should distribute evenly among a dozen liners. Divide the streusel among the muffins (use all the streusel).
Bake muffins at 400° F for 18 minutes or until a toothpick inserted in the center comes out with little to no crumbs. Let muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely before consuming. Be sure not to leave muffins in the pan for more than 5 minutes as the bottoms will get soggy.
Notes
Store strawberry muffins in an airtight container at room temperature for up to 3 days.Freeze strawberry muffins in an airtight container for up to 1 week.