After caramelizing the onions on medium-high heat for 35 minutes, I reduced the heat to medium and cooked the onions for an additional 30 minutes, until they were a deep brown. After simmering the soup and adding ample salt and freshly ground pepper, the flavor was still off, so I added a tablespoon of liquid aminos. I used dried thyme, and it was a bit overpowering, so definitely use sprigs of fresh thyme. My French onion soup crocks hold only 16 ounces, so I was able to make 6 bowls of soup. I used a gruyere and Swiss blend of shredded cheese.
You don't need to put the soup under a broiler to get an bubbly browned topping. Just put your bowls on a sheet pan and bake at 400 degrees until the cheese is a golden brown, about 12 minutes.
