These shortcakes are bursting with ripe summer fruits for a dessert that will delight the whole family.
Preheat oven to 400 degrees. In a medium bowl, whisk together flour, cornmeal, baking powder, baking soda, salt, and granulated sugar. Using the large holes on a box grater, grate butter into flour mixture. Using your fingers, incorporate butter into flour mixture, breaking it into even smaller pieces. With a fork, stir in buttermilk until dough just comes together. Lightly flour a rolling pin and work surface and roll out dough to a 3/4-inch-thick rectangle. Cut into 6 squares (or rectangles).
Place dough squares, 3 inches apart, on a parchment-lined baking sheet. Brush tops with buttermilk and sprinkle with granulated sugar. Bake until shortcakes are golden and puffed, 17 to 20 minutes. Let cool completely on a wire rack.
In a medium bowl, using an electric mixer, beat cream and confectioners' sugar on high until stiff peaks form, about 3 minutes. Cut shortcakes in half horizontally. Divide peaches among bottom halves, top with whipped cream and blueberries, and sandwich with top halves.
Be flexible with the fruit in all these desserts. Use peaches in place of nectarines, or a mixture. Store plain shortcakes, tightly wrapped in plastic, up to 2 days.