Onion powder is made from dehydrated then finely ground onions. The powder can be sprinkled on meats before cooking or incorporated into sauces, soups, or dips. Use onion powder in casseroles and meatloaf or other dishes where you want to add onion flavor and fresh is not available.
The only difference between onion powder and granulated onion is that onion powder has been ground finer.
This is a readily available grocery store item so look for it in the spice section of your local grocery store. For convenience you may want to just add it to your next Amazon order: Onion Powder.
Substitute For Onion Powder
If you don't have opion powder you can substitute per teaspoon needed:
Onions only (avoid brands with additional preservatives or ingredients). McCormick makes a good quality product.