Make the cornbread: Preheat the oven to 375 degrees F and butter a 9-by-13-inch baking dish. Whisk the eggs, buttermilk, vanilla and melted butter in a bowl. In another bowl, whisk the cornmeal, flour, granulated sugar, baking powder and salt.
Add the cornmeal mixture to the egg mixture and mix with a wooden spoon until just incorporated. Gently fold the blueberries into the batter. Transfer to the prepared baking dish and bake until a toothpick inserted into the center comes out clean, 20 to 25 minutes. Transfer to a rack and let cool completely before frosting.
Make the frosting: Beat the butter in a large bowl with a mixer on medium speed until light and fluffy. Add 3 1/2 cups confectioners' sugar in batches, alternating with the milk; continue beating until smooth. Add the maple syrup, cinnamon, vanilla, pumpkin pie spice, and nutmeg to taste. Add the remaining 1/4 cup confectioners' sugar if necessary to reach a spreadable consistency. Spread on the cornbread.
Photograph by Alison Gootee
Courtesy of Food Network Magazine