These wildly delicious Blueberry Streusel Muffins are soft, tender, fluffy and topped with cinnamon kissed streusel that has a delicious coffee cake flavor!
Preheat oven to 425℉ and line a 12-count muffin tin with paper or parchment liners.
Next prepare streusel. Melt butter and use a fork to mix in in cinnamon and sugar. Mix in flour until mixture resembles small crumbs. Set aside.
If you can, measure flour and sugar in grams using a digital kitchen scale. No scale? Use the spoon and sweep method. Fluff the flour first then gently add spoonfuls of flour to your measuring cup, using a straight edge knife/spatula to level the flour with the top of the cup.
Combine dry ingredients. In a medium bowl, whisk together flour, sugar, baking powder, baking soda, cornstarch, and salt.
In a separate bowl whisk together melted butter and oil. Add egg and vanilla and mix well. Stir or fold in sour cream until thoroughly combined.
Add wet ingredients to dry and gently fold together with a spatula until mostly combined. Once the batter is about 75% combined, add the blueberries and fold them in as well until batter is completely combined, taking care not to over-mix the batter.
Evenly divide muffin batter into lined muffin tin. Liners will be most of the way full!
Sprinkle a little streusel on top of each muffin.
Bake for 8 minutes at 425℉. After 8 minutes reduce the oven temperature to 350℉ (without opening the oven door - simply adjust the temp) and then continue to bake another 10-12 minutes or until the tops are beginning to turn golden brown and a toothpick inserted in the center comes out clean or with a few crumbs.
Allow to cool 5 minutes in muffin tin then carefully remove from pan. Allow muffins to cool completely on a wire rack and enjoy!
Notes
When it comes to the blueberries, the smaller the better! To use frozen berries, don't defrost first or they'll release too much liquid into the muffins - simply fold them in frozen, straight from the freezer. They tend to dye the muffin batter purple/blue so the muffins may be purple and streaky but still tasty.Not a fan of streusel? You can also skip it and sprinkle muffins with cinnamon sugar or coarse sprinkling sugar before baking. Or make them plain with no topping at all.Nutrition Facts below are estimated using an online recipe nutrition calculator. Adjust as needed and enjoy!