Recipe from King Arthur Flour Cookbook. You can find it here on their website, although the web directions very slightly. You can fill the muffin liner to the top, they don’t really spread.
I plopped the blueberries into each liner instead of mixing them into the batter, since my husband prefers chocolate chips to any fruit–so he gets special muffins. 😉
The Streusel topping is in the cookbook as well. If I recall off the top of my head, it’s 1/2 cup flour, 6 tbs of brown sugar, 1/2 cup of chopped walnuts, 3tbs of soft butter, pinch of salt, and 1/2 tsp of cinnamon, all mixed together with your fingers.