Make crust: Whisk together flour and salt. Using a pastry cutter or 2 knives, cut butter into flour mixture until it resembles cornmeal with some pea-size pieces. Using a fork, stir in 3 tbsp. ice water. Knead dough just until it starts to hold together (if it's too crumbly, sprinkle in remaining water). Pat into a 6-in. disk; cover with plastic wrap. Chill at least 20 minutes.
Preheat oven to 350°. Whisk together sugar, cocoa, and salt. In a separate bowl, whisk eggs well; whisk in evaporated milk and vanilla and stir into sugar mixture. Stir in pecans.
On a lightly floured surface with a floured rolling pin, roll dough into a round 1/8 in. thick and 12 to 13 in. wide. Put dough in a 9-in. pie pan. Trim edge 1 in. beyond rim and fold edge under itself so it's flush with and resting on top of rim. Crimp edge with a fork.
Pour batter into crust and bake 35 to 45 minutes, or until set and crust is golden. Serve warm.
Note: Nutritional analysis is per slice.