1. Pulse flour, sugar, cocoa, and salt in a food processor until combined. Add butter, and pulse until mixture resembles coarse meal, about 10 seconds. Add yolks and vanilla, and process until mixture just begins to hold together (no longer than 30 seconds).

2. Shape dough into a disk. Wrap in plastic, and refrigerate until firm, at least 1 hour (or up to 2 days).