Line a 6-cup jumbo muffin pan or a 12-cup standard muffin pan with silicone cupcake liners or paper cupcake liners or spray with nonstick cooking spray. Set aside
In a large mixing bowl, whisk together the flour, baking powder, and salt. Set aside.
2 ½ cups all-purpose flour, 1 tablespoon baking powder, 1 teaspoon salt
To a food processor or blender, add the melted butter, brown sugar, eggs, vanilla extract, milk, sour cream, lemon juice and lemon zest. Process until well incorporated and smooth, about 30-60 seconds.
½ cup unsalted butter, 1 cup packed brown sugar, 2 large eggs, 1 tablespoon vanilla extract, ½ cup whole milk, ½ cup full-fat sour cream, 3 tablespoons fresh lemon juice, 2 tablespoon lemon zest
Pour the wet ingredients into the dry ingredients. Gently fold with a rubber spatula or wooden spoon until no dry spots of flour are left.TIP: Overmixing will lead to dry, tough muffins instead of fluffy, tender muffins, so avoid mixing longer than needed. Add ¾ cup raspberry jam to the mixture and fold in with just a few turns, breaking up any large clumps of jam as you go. You want the jam evenly dispersed but not fully blended into the muffin batter.
1 cup raspberry jam
Fill each cup of muffin tin about ¾ of the way to the top with muffin batter. Top each with 1 heaping teaspoon of jam and swirl in with a knife or toothpick. Let the batter rest while you preheat the oven to 425ºF, about 10 minutes.Tip: Allowing the batter to rest for a few minutes yields muffins that rise much better, creating those beautifully domed tops that bakeries are known for! Bake for 7 minutes at 425ºF, then lower the oven temperature down to 350ºF for another 18-20 minutes for jumbo or another 11-12 minutes for standard muffins, or until a toothpick inserted into the center of the center muffin comes out clean.Tip: Starting the bake of these muffins at a higher temperature allows the muffins to get an initial blast of heat that helps produce beautiful domed tops with a great rise. Allow to cool in muffin tins for 10 minutes, then transfer to a wire rack to cool completely