2 tablespoons black peppercorns
1 tablespoon mustard seeds
2 teaspoons dill seeds
1 teaspoon coriander seeds
1 tablespoon plus 1 teaspoon coarse kosher salt
1 tablespoon plus 1 teaspoon dried minced garlic
1 teaspoon crushed red pepper flakes
Cook peppercorns, mustard seeds, dill seeds, and coriander seeds in a small skillet over medium heat, stirring, until fragrant and beginning to pop, about 2 minutes. Transfer to a mortar and pestle and coarsely crush, or transfer to a sturdy resealable plastic bag and coarsely crush with the bottom of a heavy skillet. Add salt, garlic, and chile flakes and crush to combine.
Spice rub can be made 1 month ahead. Store in an airtight container.