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 vegetable oil, brown sugar, eggs, vanilla extract, milk, ricotta, lemon juice and lemon zest. Blend until well incorporated and smooth, about 30-60 seconds.
⅓ cup vegetable oil, 1 cup brown sugar, 2 large eggs, 1 tablespoon vanilla extract, ½ cup whole milk, 1 cup ricotta, 3 tablespoons fresh lemon juice , 2 tablespoon lemon zest
Pour the wet ingredients into a dry ingredients. Gently fold in the dry ingredient mixture with a rubber spatula or wooden spoon until no dry spots of flour are left.
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.
1 cup raspberry jam
Allow the muffin batter to rest while you preheat the oven to 425ºF.
Bake for 7 minutes at 425ºF, then lower the oven temperature down to 350ºF for another 12-14 minutes for standard muffins and 20-22 minutes for jumbo, or until a toothpick inserted into the center of the center muffin comes out clean.
Allow to cool in muffin tins for 10 minutes, then transfer to a wire rack to cool completely