Recipe from The Pastry Queen: Royally Good Recipes From the Texas Hill Country’s Rather Sweet Bakery & Café (co-written with Alison Oresman and published by Ten Speed Press)
2 cups all-purpose flour
1/2 teaspoon salt
1/3 cup sugar
2/3 cup (10 2/3 tablespoons) chilled unsalted butter
1 large egg, lightly beaten
1/4 cup chilled whipping cream, plus more as needed
Using a mixer fitted with a paddle attachment, mix flour, salt, and sugar in a large bowl on low speed for about 30 seconds. Cut butter into 1/2-inch pieces. Add butter to flour mixture and combine until mixture forms crumbs about the size of peas, 1 to 1 1/2 minutes.
Whisk egg with cream, add to flour mixture, and combine until dough begins to clump together. Continue mixing for 10 seconds longer. If dough does not form a ball, add more cream, 1 tablespoon at a time. Mold dough into a disk, cover in plastic wrap, and refrigerate for at least 1 hour.
Roll out dough 1/8-inch thick and transfer to a 10-inch tart pan, crimping edges with your fingers or a fork.
1 1/2 cups coarsely chopped walnuts
3/4 cup (1 1/2 sticks) unsalted butter
14 ounces chopped chocolate, semisweet or bittersweet or any combination
1 1/2 cups sugar
3 large eggs
2 teaspoons vanilla extract
1/2 teaspoon salt
2/3 cup whipping cream
2 tablespoons dark rum or whiskey (optional)
Preheat oven to 350 degrees. Place walnuts on a cookie sheet and toast until a rich brown, 7 to 9 minutes.
Put butter and chocolate in a microwave-safe bowl and heat on medium-high for 1 minute. Remove from microwave and stir. If chocolate is not completely melted, keep heating in 30-second increments. Stir until blended. (Or combine butter and chocolate in a metal bowl set over a saucepan filled with 3 inches of simmering water. Stir until melted and combined, then remove bowl from saucepan.) Whisk sugar into butter-chocolate mixture. Add eggs 1 at a time, whisking until smooth after each addition. Whisk in vanilla, salt, cream, and rum or whiskey.
Spread nuts on bottom of unbaked tart crust, then pour chocolate mixture over nuts without stirring (do not fill to more than 1/2 inch below top of crust). Bake for 50 minutes. The filling will seem undercooked and jiggly in the middle, but remove tart from oven anyway; it will set as it cools. Do not cut tart until it has cooled at room temperature for at least 2 hours (or refrigerate to firm it up more quickly).