Ref: *ONIONS: A COUNTRY GARDEN COOKBOOK (1995: Collins)

ABOUT: Home-dried onions are ...typically sweeter and more concentrated.
Dried onions impart a unique sweet, deep flavor to soups or stews. Or chop
them and use as an interesting garnish for salads.

DRYING: When drying onions, use the sweetest, most pungent onions available
for the most flavorful results. To dry onions in the oven, peel and then
cut into slices 1/4 inch thick. Arrange on a rack on a baking sheet or
roasting pan and place in an oven preheated to 150F. Store in the oven,
undisturbed, for approximately 3 hours, or until the onions are brittle.