How to Make It
Prepare the crust: Whisk together flour, cornmeal, and salt in a large bowl; set aside. Beat butter and cream cheese with an electric mixer fitted with paddle attachment on medium speed until creamy and well combined, 1 minute. Add egg yolk; beat on low speed until just combined. Add flour mixture; beat on low speed until dough begins to form. Shape into a flat disk. Wrap in plastic wrap; chill 2 hours or up to 2 days.
When ready to use, remove dough from refrigerator, and let sit at room temperature until soft to the touch and easy to roll, 20 to 30 minutes. Unwrap and roll out on a lightly floured surface into a 12- to 13-inch circle. Fit dough into a 10-inch tart pan with a removable bottom. Fold edges over. Press into pan, forming an even, thick edge along sides and bringing dough 1/4 inch over top of pan. Prick bottom of dough with a fork a few times. Chill until firm, about 30 minutes.
Preheat oven to 375°F. Line dough with parchment paper; fill with pie weights or dried beans. Bake until pale golden around the edges, about 15 minutes. Remove the parchment and weights, and continue baking until bottom of crust is set, 8 to 10 more minutes. Transfer to a wire rack; cool completely, about 30 minutes.
Prepare the filling: Reduce oven temperature to 325°F. Whisk together sugar, flour, cornmeal, butter, buttermilk, orange zest, orange juice, and lemon juice until blended. Add eggs, and whisk until smooth. Pour mixture into prepared tart crust. Bake on the lowest oven rack until golden and set, 35 to 40 minutes. Cool completely on a wire rack, about 2 hours. Chill tart until cold, about 2 hours.
Prepare the gelée: Combine pomegranate juice and sugar in a saucepan. Sprinkle gelatin over mixture, and let stand 5 minutes. Cook over medium heat just until mixture is steaming and gelatin dissolves, about 5 minutes. Remove from heat; cool 20 minutes. Skim off foam, if needed. Stir in liqueur.
Gently and slowly pour pomegranate mixture over top of chilled tart until just below edge of crust, being careful not to overfill (you may have extra pomegranate mixture). Continue to chill tart until gelée sets, about 1 hour. Sprinkle with pomegranate arils just before serving.