Preheat the oven to 350°F. Line a rimmed baking sheet with a nonstick silicone mat or parchment paper.

Whisk together the flour, cocoa, baking powder, and salt in a medium bowl. Add the sugar, egg white, egg, espresso, and vanilla. Stir to combine

Drop the dough by rounded tablespoonfuls 2 inches apart on the prepared baking sheet. Top each cookie with a pecan half. Bake until just set, about 10 minutes. Remove to a rack to cool slightly then remove with a metal spatula to the rack cool completely. Store in an airtight container for up to 1 week.