Step 1

Preheat the oven to 425°F.

Step 2

Line a 12-cavity muffin pan with muffin/cupcake liners.

Step 3

In large mixing bowl, use a hand mixer to cream together the butter, granulated sugar, brown sugar, and vanilla extract on medium-high speed until smooth and combined, 1-2 minutes.

Step 4

Add the eggs and beat for a minute longer, until the mixture is pale and fluffy. Add the sour cream and milk. Continue to beat until fully incorporated, scraping down the sides of the bowl with a rubber spatula.

Step 5

Add the flour, baking powder, baking soda, cinnamon, and salt to the bowl. Beat the mixture on medium-low speed, scraping down the sides of the bowl with a rubber spatula as needed, until just combined. Do not over-mix.

Step 6

To make the streusel, place the flour, brown sugar, granulated sugar, cinnamon, and salt in a large mixing bowl. Stir with a fork to combine. Drizzle the melted butter into the bowl, and mix with the fork until the mixture forms large crumbs.

Step 7

Fill each muffin liner approximately 1/3 full with muffin batter. Crumble a scant tablespoon of streusel into each muffin cup. Divide the remaining batter into the muffin cups. Sprinkle the muffins with the remaining streusel.

Step 8

Bake the muffins on middle rack of oven for 5 minutes.

Step 9

Reduce the oven temperature to 350°F. Continue baking until a toothpick inserted in the center of a muffin comes out clean, 14-16 minutes.

Step 10

Check to see that muffins are done. Remove from oven or add time as needed.

Step 11

Allow the muffins to cool in the pan for 5 minutes before removing and serving. Store leftovers in an airtight container at room temperature for 2 days, or refrigerate for 3 days.