I had to make some changes to the recipe because the strawberry gelee (the filling) tasted horrible with powdered gelatin. I had to redo the filling by puree-ing frozen strawberries and did a reduction to make it thicker. So instead of thickening the sauce with gelatin, I just simmered it much longer.
Overall, this cupcake was awesome. There are 3 parts: cupcake, filling, and frosting. I LOVED IT! Here's the tweaked recipe.
Magnolia Bakery’s Vanilla Cupcakes
1 1/2 cups self-rising flour
1 1/4 cups all-purpose flour
1 cup (2 sticks) unsalted butter, softened
2 cups sugar
4 large eggs, at room temperature
1 cup milk
1 teaspoon pure vanilla extract
Directions:
Preheat oven to 350 degrees. Line two 12-cup muffin tins with paper liners; set aside. In a small bowl, combine flours; set aside. In the bowl of an electric mixer fitted with the paddle attachment, cream butter until smooth and creamy. Gradually add sugar, beating until fluffy, about 3 minutes. Add eggs, one at a time, beating well after each addition. Add dry ingredients in 3 parts, alternating with the milk and vanilla, and scraping down sides of bowl in between each addition; beat until ingredients are incorporated but do not overbeat.
Divide batter evenly among liners, filling about three-quarters full. Bake, rotating pan halfway through, until a cake tester inserted in the center comes out clean, 20 to 25 minutes.
Transfer to a wire rack to cool in tins for 15 minutes. Remove cupcakes from tins, and cool completely on rack. Once cupcakes have cooled, frost as desired.
Makes about 2 dozen cupcakes.
Strawberry Filling
1 cup strawberry puree
1/4 cup sugar
1 tablespoon lemon juice
1/2 cup diced, fresh strawberries
Directions:
Heat puree and sugar in a small saucepan just until it begins to bubble, stirring to dissolve sugar. Stir in lemon juice and remove from heat. Stir in diced strawberries and chill until set.
Strawberry Mascarpone Frosting
1/4 cup softened butter

1 8 ounce container mascarpone, at room temperature
1/2 cup fresh strawberries, pureed
2 tablespoons strawberry jam
2-3 cups powdered sugar
Directions:
Cream butter and cream cheese in an electric mixer until soft and fluffy, about 2 minutes.
Add the strawberries and jam. Mix until combined. Add the powdered sugar, 1 cup at a time until the frosting has the sweetness and consistency you desire. If your frosting is not stiff enough to pipe, add more powdered sugar.