slice the onions into 1/2" pieces. Try to keep them as even as possible
melt all the butter in the pot on medium-low heat, add the onions and season liberally with salt. Simmer un-covered for about 30 minutes, tossing with tongs every 5-10 minutes until the onions are submerged in their own juices / butter
Continue to simmer the onions on medium low for another 30-40 minutes until they darken, but still have some crunch to them.
stir in the wine, thyme, pepper, bay leaves and simmer covered for 5 minutes
Add the broths, bring to a boil on high then reduce to low, cover to a small crack and simmer for 45 minutes, stirring occasionally
adjust the seasoning with Worcestershire and lemon juice as desired then continue to simmer covered to a crack for another 45 minutes.
Ladle the soup into small bowls, add 1-2 toasted baguettes, top with cheese and broil 2 minutes