"The slow cooker completely eliminates the stirring part of caramelizing onions; it all goes happily unattended. Freeze the bag of soup in a bowl rather than laying it flat, so it will fit in the saucepan when it's time to thaw...."
INGREDIENTS
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1/4 cup unsalted butter
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6 thyme sprigs
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1 bay leaf
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5 pounds large sweet onions, vertically sliced (about 16 cups)
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1 tablespoon sugar
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6 cups unsalted beef stock (such as Swanson)
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2 tablespoons red wine vinegar
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1 1/2 teaspoons kosher salt
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1 teaspoon black pepper
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24 (1/2-ounce) slices whole-grain French bread baguette