How to Make It
Prepare the Blueberry Filling: Combine preserves, blueberries, and butter in a small saucepan over medium-high, and bring to a boil. Cook, stirring often, until berries begin to break down, about 4 minutes. Stir together cornstarch and water in a small bowl, and add mixture to pan. Cook, stirring constantly, until thickened, 1 to 2 minutes. Transfer Blueberry Filling from pan to a bowl, and cool completely, about 20 minutes.
Prepare the Cupcakes: Preheat oven to 350°F. Beat butter and cream cheese with an electric mixer on medium speed until creamy and smooth, about 1 minute. Gradually add sugar, and beat until light and fluffy, 3 to 4 minutes. Add eggs, 1 at a time, beating until blended after each addition. Beat in vanilla.
Combine flour, baking powder, baking soda, and salt. Gradually add to butter mixture alternately with buttermilk, beating just until blended after each addition. Place 12 paper baking cups in a 12-cup standard-size muffin pan, and divide batter evenly among baking cups (filling about three-fourths full). Bake in preheated oven until a wooden pick inserted in centers comes out clean, 15 to 17 minutes. Cool in pan on a wire rack 5 minutes. Transfer from pan to wire rack, and cool completely, about 30 minutes.
Prepare the Frosting: Beat cream cheese and butter on medium speed until creamy and smooth. Beat in lemon juice and salt. Gradually add powdered sugar, and beat at low speed until smooth, 1 to 2 minutes. Gradually beat in cream until spreadable consistency is reached.
To fill Cupcakes, carefully scoop out centers, using a 1-inch melon baller and leaving a 1⁄2-inch border around edges (hole will be about 1 inch deep). Discard or reserve cake centers for another use. Spoon or pipe 1 tablespoon of Blueberry Filling into center of each Cupcake.
Pipe or spread Frosting on top of each. Arrange fresh strawberries and blueberries on tops of Cupcakes before serving.