Combine the dried dill, whole coriander, sea salt, dill seeds, powdered onion, ground yellow mustard, and garlic powder in a spice grinder. Grind everything together until you achieve a fine, even powder. I like to pulse the grinder a few times at first to break down the larger spices before letting it run continuously until everything is nicely blended.

Carefully transfer your freshly ground seasoning mix from Step 1 into a small, sealable container. Store in a cool, dry place until ready to use. Keeping it in an airtight container will help preserve its flavor and aroma for longer.