Yield: 1 9-inch tart
1 pie crust for a 9 or 10-inch pie (or see crust recipe below)
1 (12-ounce) bottle Traveler Grapefruit Shandy
1 cup freshly squeezed ruby grapefruit juice, seeds removed
Zest of 2 grapefruits (about 2 tablespoons; use a microplane grater, or zest and chop very fine)
2/3 cup sugar
6 large whole eggs
6 large egg yolks
1 stick (8 tablespoons) unsalted butter, cut into pieces
Pinch of salt
1/2 teaspoon pure vanilla extract
4 tablespoons grapefruit or orange marmalade, for glaze (optional)
Fresh mint or seasonal berries, for garnish (optional)
Roll the pie crust out in a 10 1/2-inch circle, and line a 9-inch tart pan with removable bottom. Prebake according to package directions. Set aside.
In a saucepan, bring the Traveler Grapefruit Shandy to a low boil and cook until reduced to 1/2 cup, 20 to 25 minutes. Pour into bowl. Pour the grapefruit juice into the saucepan and reduce to 1/2 cup, 5 to 10 minutes. Pour into the bowl with the Shandy and set aside.
Fill a large bowl with water and ice cubes. Set aside.
Put the sugar, eggs, yolks and salt into the top of a double boiler set over (not in) boiling water. Whisk constantly until thickened. Add the Shandy and grapefruit juice reductions and keep whisking until thickened again. Remove from heat and add the butter chunks and vanilla extract, whisking until butter is melted. Place gently into the prepared cold water bath and whisk until cool. Use immediately or cover with plastic wrap and refrigerate up to 24 hours.
To bake: Preheat oven to 400 degrees F. Spoon the custard into prebaked crust and smooth the top. Bake until the filling is set and slightly golden, 20 to 25 minutes. Cool to room temperature. Release tart from the rim of the pan and serve, or cover and chill up to 24 hours.
Just before serving, warm the marmalade, if using, and strain into a cup. Gently brush or spoon over the surface of the tart.
To make the crust: Place 1 and 1/2 cups all-purpose flour, 2 1/2 tablespoons sugar, finely grated zest from one grapefruit, and a pinch of salt into a food processor and pulse to mix. Add 8 tablespoons chilled butter and process until it is the texture of rolled oats. With the motor running, drizzle in 2 to 3 tablespoons chilled red grapefruit juice or ice water, until the mixture comes together and forms a dough. Form into a disc, wrap in plastic wrap, and refrigerate for up to 3 days. When ready to bake, fit crust into a tart pan as described above. Preheat the oven to 400 degrees F. Line the tart shell with a sheet of buttered foil, butter-side down. Weigh down with dried beans, rice or pie weights, and bake 8 to 10 minutes. Carefully lift out the foil and weights. Prick the dough all over with a fork. Cover the edges with foil to prevent over-browning and bake 8 minutes longer. Fill and bake as directed.