These tender, sweet but not too-sweet muffins are as easy to make as they are to love. Bring them to your next brunch/picnic/party host/day at work. (January 2017 Update: The recipe now has the original amount of topping again! I'd doubled it but changed my mind again -- this is the way we prefer it.)
Preheat oven to 350°F with a rack in the center. Line 18 standard muffin cups with paper liners or grease the pan well with oil or cooking spray, including the top.
In a medium bowl, stir together the 2 cups flour, baking powder, baking soda and 1/2 teaspoon salt.
In a small bowl, stir together the yogurt and vanilla extract.
In the bowl of a stand mixer (or a large bowl), beat together the 4 tablespoons butter and the 1 cup sugar until lightened in color and texture, about 3 minutes. Add the eggs and beat to incorporate. Then add half the flour mixture and beat on low until just incorporated. Follow with half the yogurt mixture and then the remaining halves of the flour and yogurt, beating on low after each addition. Fold blueberries into the batter. Spoon by the scant 1/4-cupful into paper-lined muffin cups.
To make the crumble topping, stir together the flour, brown sugar, nuts, cinnamon and salt in a small bowl. Pour the melted butter overtop and stir to incorporate into the dry ingredients. Cover the surface of each muffin with topping and press lightly.
Bake for about 24 minutes, until a tester comes out almost clean. Remove muffins to a wire rack to cool.
* I like to use lightly sweet Siggi's vanilla skyr.