Blueberry Sweet Corn Shortcake

Bring lemon zest and juice, cornstarch, 4 cups blueberries, 1/2 cup granulated sugar, and 1/4 teaspoon salt to a simmer in a medium saucepan over medium. Cook, stirring occasionally, until berries begin to burst and liquid is syrupy, about 10 minutes. Transfer to a medium heatproof bowl and stir in remaining 2 cups blueberries. Set aside to cool for 30 minutes. Refrigerate, uncovered, until cold, about 1 hour. 

While berry mixture cools, preheat oven to 350°F. Lightly coat a 13-by-9-inch baking pan with cooking spray. Line bottom and sides with parchment paper, leaving a 2-inch overhang on short sides. 

Grate corn ear to remove kernels, using largest holes on a box grater set inside a large bowl; discard cob. Whisk eggs, oil, vanilla, 1 cup buttermilk, and remaining 1 1/2 cups granulated sugar in large bowl with corn pulp. Add flour, cornmeal, baking powder, and remaining 1/4 teaspoon salt; whisk until combined. Transfer mixture to prepared pan. Use a rubber spatula to spread into an even layer. 

Bake until a wooden pick inserted in center comes out clean, about 30 minutes. Remove cake from pan, using parchment paper as handles. Let cool completely on a wire rack, about 1 1/2 hours.  

When ready to assemble, beat cream and confectioners’ sugar with an electric mixer on medium speed until medium peaks form, 2 to 3 minutes. With mixer on medium speed, drizzle in remaining 1/2 cup buttermilk and beat until medium-stiff peaks form, about 30 seconds.

Cut cooled cake in half horizontally. Place bottom half, cut side up, on a platter. Spoon about 2 cups cooled berry mixture over bottom cake layer and top with about 2 cups whipped cream. Gently cover with top cake layer, cut side down. Spread remaining 2 cups whipped cream over cake, then spoon remaining 2 cups berry mixture over top. Slice and serve immediately. (Alternatively, top each individual slice with berry mixture.)