Preheat your oven to 425F degrees and grease or line two 12-cavity muffin pans.

In a small bowl, toss together the streusel ingredients. Set aside. Then in a separate medium bowl, whisk together the flour, baking powder, baking soda and salt in a medium bowl.

In a large bowl using a hand-held or stand mixer, beat together the butter and sugar on medium speed until creamy - about 1 minute. Then add in the eggs and vanilla and continue beating until combined for about 30 seconds. Turn off your mixer, scrape down the sides of your bowl, and fold in the sour cream and milk with a large rubber spatula.

Very carefully, fold in the flour mixture until almost combined. Then slowly fold in the blueberries. The batter will be very thick with some lumps remaining.

Using a 1/3 dry measuring cup, scoup & pour batter into muffin tins filling each cavity to the very top. You should get about 14-16 muffins. Place a few blueberries on the top of each muffin & sprinkle with streusel topping.

Bake in the oven for 5 minutes on 425F degrees, then turn down your oven to 375F and cook for an additional 11-14 minutes until tops are slightly browned and a toothpick comes out clean.