Spread the Cheddar in a thin, even layer on a microwave-safe plate lined with parchment. Microwave in 30-second intervals until the cheese has melted into a firm disc and the fat has rendered out, about 2 minutes.
Allow the cheese disc to cool slightly, then peel from the parchment and place on a paper towel to cool completely. It will crisp as it cools.
Once the cheese disc is completely cooled, break it into pieces. Pulse it in a food processor until finely and evenly ground, about 45 seconds. Add the cornstarch and pulse again just to incorporate.
Store in an airtight container in the refrigerator for up to 3 weeks. Use to flavor popcorn, vegetables, noodles or anything else you would add cheese to!
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