Lightly coat an 11-inch, removable bottom tart pan and set aside.

In a medium-size bowl, using a spatula or wooden spoon, mix the powdered sugar, vanilla, egg yolks and sea salt. Add the cooled butter and mix to a smooth consistency then, add the flour and cornstarch and stir until the dough forms a smooth ball.

Press the dough into the bottom and up the edges of the prepared tart pan. Smooth the crust with the flat bottom of a measuring cup or flat-bottomed glass. 

Prick the crust with a fork, place on a baking sheet and transfer to the freezer for 30 minutes.

Remove the crust from the freezer, spray a piece of aluminum foil with non-stick spray and press the sprayed side of foil very tightly up against the bottom and up the sides of the crust. Add pie weights and transfer to the middle rack of the oven.

Bake for 15 minutes. Remove foil and continue to bake uncovered for another 10 minutes, or until golden brown. Remove from the oven and let cool on a wire rack.

Reduce the oven to 325°F

Beat the eggs, egg yolks and sugar together with electric mixer until well combined. Add the eggnog, salt, vanilla, rum and vanilla. Beat on low speed until well blended. 

Set a fine-mesh strainer over a large bowl and pour the mixture through to stain out any egg residue. 

Set the cooled tart crust on a baking sheet lined with parchment paper and pour the strained eggnog mixture into the crust. Grate nutmeg over the top and transfer to the middle of the oven. 

Bake the tart until the filling is set but still jiggles slightly in center, 55 to 60 minutes (filling will continue to set as it cools). Transfer to a cooling rack and cool for 30 minutes. Refrigerate and chill tart, uncovered, until cold, at least 2 hours. Just before serving release the side of the pan and transfer to a serving plate.