Preheat oven to 425°F. Lightly spray 12 muffin cups with non-stick cooking spray or line with muffin liners.
In a medium bowl, whisk together flour, baking soda, baking powder, and salt. Set aside.
In a large bowl, using an electric or stand mixer combine brown sugar, butter, egg, vanilla extract, and buttermilk, mix until combined.
Mix flour mixture until just combined. The muffin batter will be thick.
Gently, fold in raspberries.
MAKE THE CRUMBLE:
In a small bowl, mix together sugar, flour, cinnamon, and butter until the mixture becomes crumbly. Set aside.
Using an ice cream scooper, scoop muffin batter into prepared muffin tins. Sprinkle each muffin with the crumb mixture. Using the 1/4 cup of the raspberries you have leftover, press a few of them into the tops of each muffin.
Bake at 425°F for 5 minutes. Keeping the muffins in the oven, reduce the oven temperature to 350°F and continue to bake for 12-15 more minutes or until a toothpick inserted in the center comes out clean.
Let muffins cool for 5-10 minutes before enjoying!
Notes
Use Fresh or Frozen Raspberries: Both work well, but if using frozen raspberries, don’t thaw them before adding to the batter to prevent them from bleeding and turning the batter pink.
Gently Fold in Raspberries: Mix raspberries into the batter gently to avoid breaking them up too much. This helps keep the raspberries intact and evenly distributed.
Balance Sweetness and Tartness: Raspberries are naturally tart, so adjust the amount of sugar in the recipe to balance the flavors. You can also sprinkle a little sugar on top before baking for a sweet crust.
Add a Zesty Twist: Incorporate lemon zest or a bit of lemon juice into the batter. The citrus enhances the raspberry flavor and adds a refreshing note. Try my Raspberry Lemon Poppyseed Muffins.
Avoid Overmixing: Mix the batter just until the dry ingredients are moistened. Overmixing can result in tough, dense muffins. The batter should be slightly lumpy.