Step 1

Preheat the oven to 170°F and line two baking sheets with parchment paper.

Step 2

Peel each onion, and, using a cheese grater, grate each onion. This should yield about 4 cups.

Step 3

Transfer the grated onions to a fine wire mesh strainer that is over a bowl and squeeze out as much liquid as you can by gently pressing the onions with a spoon or your hands. (I was able to get about a cup of liquid.) Store the liquid in a sealed container, in the refrigerator, for up to two weeks.

Step 4

Divide the onions in half and lay them out in a thin layer on each of the parchment-lined baking sheets.

Step 5

Bake for 5 hours, or until completely dry. The onions will turn pink; this is normal. Please note that baking times may vary. You know the onions are dry when they crumble in your hand.

Step 6

Let the dried onions cool completely before grinding them.

Step 7

To grind the onions, place them in a food processor, and grind them down to your desired consistency. You can also use a mortar and pestle for an even finer grain.

Step 8

Store the powder in an airtight container with a few grains of uncooked rice added to the powder to absorb any excess moisture.