Clean onions, well-cutting off all unnecessary.

Cut the onion into quarters.

Separate the layers from each other and spread on a grate or baking pan then place in oven and bake at a temperature of 100-150 degrees for about 2 hours. I do this often in aerogrill at a temperature of 90 degrees, about the same amount of time. As prompt in comments, you can still use the dryer for vegetables! In this case, focus on the kind of onion slices.

An indication that the onion slices are ready, is a characteristic crunch when you try to break a slice - it should be completely dried. Slices can be of different thicknesses, so be prepared for the fact that some cook sooner than others, and some will have to leave on a little longer.

Crispy onion "chips" then grind in a mortar or spice mill. I first use the mortar, so that the pieces become smaller, and then pour into the mill - when you need it powder - just use the mill. By the way, the onions after drying is sweet! All of the bitterness literally disappears.

Here's the onion powder can be used as spices for various dishes! You can pour it into a jar and add salt, there is a very good seasoning for salads, soups, meat, you can add it to the batter or sprinkle on crackers. A very useful thing!