For the topping:
1/2 c all-purpose flour
1/2 c sugar
1/2 stick unsalted butter, cut into small pieces, at room temperature
For the muffins:
Non-stick spray for the pans
2 3/4 c all-purpose flour
3 tsp. baking powder
1 1/4 tsp. baking soda
1/2 tsp. salt
1 stick unsalted butter at room temperature
1 1/2 c sugar
4 large eggs
1/2 tsp. vanilla extract
1 1/2 c sour cream
2 1/2 c raspberries, fresh or frozen
Place rack in the middle of the oven and preheat to 375 F.
To make the topping: Mix the flour and the sugar together in a medium bowl until blended. Add the butter and using your hands or a fork, mix the ingredients until crimbly. Set aside.
To make the muffins: Spray 18 regular muffins with non-stick spray (Pam or vegetable oil); Whisk the flour, baking powder, baking soda, and salt together in a medium bowl until blended, and set aside.
Beat the butter and sugar together on medium speed with a handheld or stand mixer fitted with the paddle attachment until light and fluffy, about 3 minutes. Add the eggs, one at a time, mixing the batter on low speed until smooth after each addition and scraping down the sides and bottom of the bowl if necessary. Add the vanilla, and mix to combine.
Add about one-third of the dry ingredients to the batter, and mix on low until blended. Add half of the sour cream, mix and repeat with another third of the dry ingredients, the rest of the sour cream, and the remaining dry ingredients, mixing between each addition. Use a spatula to fold in the raspberries by hand.
Fill the prepared muffins tins until almost full, and sprinkle 1 tbsp. of the topping onto each muffin (don't worry if it looks like a lot of topping).
Bake the muffins for 25 to 30 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Cool the muffins in the pan for 5 minutes. Using a kitchen knife, gently lift the muffins out of their tins and transfer to a cooling rack.