Preheat oven to 375 degrees F. Line a cupcake pan with paper liners.
In a large bowl, combine oil, sugar, egg, sour cream, and vanilla.
Stir in salt and baking powder. Gradually add flour a little at a time until just combined. Do not over mix.
Evenly divide batter between muffin liners ,filling each ~⅔ of the way full.
For the Brown Sugar Streusel
In a medium bowl, whisk together flour and brown sugar.
Cut in butter with 2 forks until the mixture resembles coarse crumbs.
Top each muffin with a few raspberries. Cover with streusel topping ~1-2 tablespoons each.
Bake for 20-22 minutes or until a toothpick inserted in the center comes out clean.
Cool for 5 minutes in pan. Remove to a wire wrack to cool completely.
Notes
Ingredient Notes
Flour: Measure correctly by spooning it into your cup and leveling with a knife. Scooping directly from the bag can pack in a lot more flour, leading to dense, dry muffins.
Baking Powder: Use double acting baking soda.
Sour Cream: Use full fat for the best results. Greek yogurt works as a substitute, but sour cream gives better flavor.
Raspberries: Look for berries that are plump and deep red to ruby red in color. Pale tips usually mean they're underripe and will taste tart. Avoid packages with lots of liquid pooling at the bottom. Always be sure to pat dry with paper towels after washing.
Eggs: Room temperature eggs mix more smoothly into the batter. Set them out 30 minutes before baking. Forgot to plan ahead? Place in a bowl of warm water for 5 minutes.
Butter: Use cold not room temperature butter for the streusel to form those big chunky crumbs we all love.
Krystle's Tips
Prevent Berries From Sinking: Toss berries with a few teaspoons of flour to evenly disperse them throughout the batter.
Don't Overmix: Gently mix ingredients just until combined. Overmixing develops too much gluten, making muffins tough.
Rest Batter: Rest batter for 10 minutes before scooping into muffin tins.
Use An Ice Cream Scoop: This will give you muffins that are the same size. Aim for around ¼ cup of batter per muffin or until the tin is about ⅔ of the way full.
Don't Overbake: Bake until a toothpick inserted in the center comes out with just a few moist crumbs.