I tried and failed to carmelize onions last night. Why didn't they brown? I followed Julia Child's instructions from The Way to Cook, which has you cook them with the lid on for 10 minutes and then add salt and sugar and cook with the lid off. I used a Le Creuset cast iron pot and it was bubbling evenly across the bottom, meaning that I believed the heat was high enough to produce carmelization but not so high that the onions would burn before carmelizing. I kept at it for about an hour and a quarter but then the onions started to break down and I decided I needed to get on with the second phase of the project or we'd never eat dinner. Any suggestions of what I should have done differently?