In a small bowl, whisk together the kosher salt and light brown sugar, breaking up any sugar clumps with a fork.
Add the cornstarch, garlic powder, onion powder, turmeric, paprika, chili powder, and black pepper to the bowl.
Stir all spices until the mixture is uniform in color and texture.
Transfer the rub to an airtight spice jar or resealable bag.
Store in a cool, dry place for up to 6 months for maximum freshness.
To use, pat steaks dry with a paper towel and apply the rub generously to all sides at least 30 to 40 minutes before grilling to allow the salt to penetrate the meat.