Preheat and prep: preheat your oven to 375°F and line a 12-cup muffin pan.
Stir together dries: use a fork to stir together all the dry ingredients in a small bowl.
Mix in butter: add melted butter to dries and use a fork to blend until crumbs form and there are no more dry patches in the mixture.
TO MAKE THE MUFFIN BATTER:
Cream butter, sugar, and extract: cream butter, sugar, and vanilla extract using a hand or stand mixer for about 1 minute on medium-high speed until light and fluffy.
Beat in eggs: add eggs and beat another minute on medium until batter is smoothed out a bit and well-combined.
Alternate dry and sour cream additions: combine the dry ingredients and blend together in a small bow. Add half the dry ingredients to your batter, then all the sour cream, then the other half of the dry ingredients, mixing on low between batches to just until incorporated. (Be sure to scrape the bowl well between each addition too!)
Fold in blueberries: using a spatula, gently fold or mix in blueberries just until evenly distributed. (see notes)
Divide and top: divide the batter evenly between prepped muffin cups (about ¼ cup batter each). Generously sprinkle streusel over top of each muffin to form an almost solid layer.
Bake: Bake muffins at 375°F for 20-22 minutes until golden brown, and the tops feel fully set when gently pressed.
Cool, share, and enjoy: cool muffins for 10-15, then loosen edges with an offset spatula as needed, before fully transferring to a wire rack. Share with family and friends for breakfast, a coffee break, or the tastiest afternoon snack in town!
Test Kitchen Tips
Frozen blueberries: If using frozen blueberries, be sure to keep them frozen until right before you mix them in your batter or you will definitely end up with some purple muffins!
Extra blueberries: You can add more blueberries if you'd like, just know you'll need to increase your yield to 13-15 muffins depending on how many extras you add.
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