Step 1

Preheat oven to 175ºF.

Step 2

Crumble grounds up with your hands and spread out in a thin, even layer on a baking sheet.

Step 3

Place baking sheet in the preheated oven and bake for 1-3 hours, tossing every hour or so, until the grounds feel dry and slightly crunchy. The exact amount of time this takes will depend on how much of the grounds you start with.

Step 4

Using a coffee grinder, further grind into a fine powder; you may need to do this in batches.

Step 5

Store in an airtight container in a cool, dry place. Keeps for at least a year.