Toast walnuts in a dry skillet over medium heat until fragrant, 3–4 minutes. Cool, then chop finely.
Whisk flour, cocoa, baking powder, salt, and espresso powder in a medium bowl.
In a large bowl, whisk granulated sugar, brown sugar, oil, eggs, and vanilla until glossy and smooth.
Fold dry ingredients into the wet mixture just until no dry streaks remain.
Stir in chopped walnuts. Cover and chill the dough until firm, about 1 hour.
Preheat oven to 350°F. Line two baking sheets with parchment paper.
Scoop 1½-tablespoon portions. Roll each in granulated sugar, then coat generously with powdered sugar.
Arrange on sheets 2 inches apart. Bake 10–12 minutes, until crackled and just set at edges.
Cool on the pan 5 minutes, then move cookies to a rack to finish cooling.
Notes
Variation: Add 1/2 tsp ground cinnamon or 1 tsp orange zest to the dry mix for a warm or citrusy twist. Storage: Keep in an airtight container at room temperature up to 4 days, or freeze baked cookies for 1 month. For make-ahead, freeze scooped dough balls; thaw slightly, then roll in sugars and bake.This recipe is an original creation inspired by classic Walnut Crinkle Cookies Recipe flavors. All ingredient ratios and instructions are independently developed.