Prepare the pastry: In a large mixing bowl, combine 2 cups flour with 1/4 teaspoon salt. Cut in 10 tablespoons cold butter using a pastry cutter or fork until mixture resembles coarse crumbs. Add 4-5 tablespoons ice water, one tablespoon at a time, mixing until dough just comes together. Form into a disk, wrap in plastic, and refrigerate for 30 minutes.

Prepare tamarind: Extract pulp from 12-15 tamarind pods by removing shells and removing seeds. Soak pulp in 1 cup warm water for 15 minutes, then press through a fine-mesh strainer to extract smooth pulp. Discard fibers and seeds. You should have about 3/4 cup tamarind concentrate.

Make filling: In a medium saucepan over medium heat, combine tamarind concentrate, 1 cup brown sugar (packed), 3 beaten eggs, 1/2 cup melted butter, 1 teaspoon vanilla extract, 1/2 teaspoon cinnamon, 1/4 teaspoon nutmeg, and zest from 1 lime. Whisk constantly until mixture thickens slightly, about 5 minutes. Remove from heat and let cool for 10 minutes.

Preheat oven to 350°F (175°C). Roll out chilled dough on a floured surface to 1/8-inch thickness. Transfer to a 9-inch tart pan with removable bottom, pressing dough into corners and trimming excess. Prick bottom with a fork.

Pour cooled tamarind filling into prepared crust, spreading evenly. Place tart pan on a baking sheet.

Bake for 40-45 minutes until filling is set but still slightly jiggly in center and crust is golden brown. The filling will continue to firm as it cools.

Remove from oven and cool completely on a wire rack, at least 2 hours. Once cooled, carefully remove outer ring of tart pan.

Optional garnish: Dust lightly with powdered sugar or serve with dollops of whipped cream. Slice into 8 wedges and serve.