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Preheat oven to 425°F (218°C). Set out 14 cupcake liners in a muffin pan. Set aside.
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Mix all of the streusel ingredients together in a small bowl using a fork to ensure there are no brown sugar clumps. Set aside.
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Whisk the flour, baking soda, baking powder, and salt together in a large bowl.
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Using an electric mixer, beat the butter, granulated sugar, and brown sugar together on high speed until smooth and creamy, about 2 minutes. On medium speed, add the eggs one at a time, beating well after each addition. Beat in the sour cream and vanilla extract on medium speed until combined. With the mixer running on low speed, add the dry ingredients and milk into the wet ingredients and beat until combined. Fold in the blueberries.
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Spoon the batter into liners, filling them all the way to the top. Top each with a scoop of streusel, gently pressing it down into the surface so it sticks. Bake for 5 minutes at 425 then, keeping the muffins in the oven, reduce the oven temperature to 350°F, and bake for an additional 18-20 minutes or until a toothpick inserted in the center comes out clean. Allow the muffins to cool for at least 30 minutes before serving.