In a medium bowl, combine 1/3 cup all-purpose flour and 1/3 cup granulated sugar. Then, add in 2 tablespoons unsalted butter, cold and cubed. Using a pastry blender or two forks, mix until the mixture resembles coarse meal. Place it in the fridge to chill while you prepare the muffin batter.
Preheat your oven to 400 degrees Fahrenheit. Line a 12-cup muffin tin with paper liners and set it aside for later.
In a large bowl, sift together 2 and 1/2 cups all-purpose flour, 3 teaspoons baking powder, and 1/2 teaspoon salt. This step helps to aerate the dry ingredients and prevents clumping.
In another large bowl, whisk together the melted 8 tablespoons (4 ounces) unsalted butter, 1 cup granulated sugar, 2 large eggs, 2 teaspoons pure vanilla extract, 1 cup full-fat sour cream, 1/2 cup lemon juice, 1 teaspoon lemon zest, and 1/2 teaspoon lemon extract (if using). Mix until everything is fully incorporated and smooth.
Add the dry mixture to the wet mixture gradually. Using a rubber spatula, gently fold until just combined. Be careful not to overmix, as this can lead to tough muffins.
Next, fold in the 1 and 1/2 cups raspberries until evenly distributed throughout the batter. It might get a little messy, but that’s all part of the fun!
Divide the batter evenly among the prepared muffin tins, filling each cup all the way to the top. It’s okay if they seem full; they’ll rise beautifully in the oven.
Now, sprinkle each filled muffin tin mold with a teaspoon or two of your chilled crumb topping from the fridge.
Bake in your preheated oven for about 22 minutes, or until the tops are puffed up and lightly golden brown. You can check for doneness by inserting a toothpick in the center; it should come out clean or with a few moist crumbs attached.
Once baked, let the muffins cool in the pan for at least 5 minutes before transferring them to a cooling rack. Enjoy warm, or store in an airtight container for up to 2 days.
For an optional glaze, in a small bowl combine 1/2 cup confectioners' sugar, 1 tablespoon lemon juice, and 1/2 teaspoon lemon zest. Whisk until smooth, adding more lemon juice if needed to achieve your desired consistency. Drizzle over the muffins right before serving.
