In a mixing bowl, combine cold cubed butter, granulated sugar, all-purpose flour, and a pinch of salt using a pastry cutter until the mixture resembles coarse crumbs. Press the dough evenly into a tart pan, ensuring the sides are well-covered. Chill the tart shell in the refrigerator for 30 minutes, then blind bake it in a preheated oven at 350°F for 25 minutes or until golden brown. Allow to cool completely.

In a medium saucepan, whisk together whole milk, heavy cream, egg yolks, granulated sugar, cornstarch, nutmeg, and cinnamon over medium heat. Stir constantly until the mixture thickens and coats the back of a spoon, about 8-10 minutes. Once thickened, remove from heat and stir in pure vanilla extract and optional alcohol. For a silky texture, strain the custard into the cooled tart shell.

Cover the filled tart with plastic wrap and place it in the refrigerator. Chill for at least 4 hours or until the custard is fully set and firm to the touch.

In a heavy saucepan, heat granulated sugar over medium heat until it melts and turns a deep amber color, about 10 minutes. Swirl the pan gently, avoiding stirring that could crystalize the sugar. Once reached, pour the caramel onto a sheet of parchment paper and let it cool completely until hard. Break it into shards for your tart’s topping.

Just before serving, adorn the chilled Eggnog Crème Tart with the caramel shards, arranging them artistically on top. For a festive touch, consider adding a dollop of whipped cream and a sprinkle of cinnamon.