How to Make It
Preheat oven to 300°F. Beat flour, sugar, coffee granules, milk powder, cornstarch, and salt with a heavy-duty electric stand mixer fitted with the paddle attachment on low speed until combined. With mixer running, drizzle in butter and coffee extract until evenly moistened, about 10 seconds. Remove bowl from mixer and continue stirring by hand, if necessary, until uniform.
Scatter mixture in a single layer on a parchment paper–lined rimmed baking sheet. Bake, stirring every 10 minutes with a metal spatula, until completely dry, about 40 minutes. Cool mixture on baking sheet. Sift through a colander, and discard fine crumbs. Store in an airtight container.