How To Make French Onion Soup in the Slow Cooker

INGREDIENTS

3 lb

yellow onions, peeled, sliced, and cut into quarter-moons

2 tbsp

unsalted butter, melted

2 tbsp

olive oil

2 tsp

kosher salt, plus more as needed

Freshly ground black pepper

10 cups

reduced-sodium beef broth

2 tbsp

balsamic vinegar

3 tbsp

brandy (optional)

etc