4-6lbswhite, yellow, sweet, and red onionspeeled and thinly sliced
3Tbspolive or vegetable oil
salt and pepperto taste
1/2cupcooking sherry or other dry white wine
4sprigsfresh thyme or 1 tsp dried
8slicesdry french bread
Transfer all of the thinly sliced onions to the slow cooker — the slow cooker should be half to three-quarters full. Cook for 5 hours on HIGH or 10 hours on LOW.
Stir occasionally, if possible — this will help them cook more evenly but is not necessary.
After 5-10 hours, the onions will be golden-brown and soft, and they will have released a lot of liquid. Remove onions to a large bowl and let cool.
If you like onions with a deeper color, continue cooking for another 3 to 5 hours on LOW. Leave the lid ajar so the liquid can evaporate. Check every hour and stop cooking whenever the onions look and taste good.
Stir sherry, Worcestershire sauce and beef broth into the remaining onions in the slow cooker bowl.
Add garlic, thyme, bay leaf and set on high for 4-6 hours OR low for 8-10 hours.
Discard bay leaf and ladle the soup into oven-safe bowls.
Top with dry bread slices and distribute Gruyere cheese evenly over each piece. Broil 2-3 minutes or until cheese is melted and browned.
Recipe provided for the National Onion Association by chef and blogger Nikki Miller-Ka.