Remove outer skin from onions, slice in half and slice very thinly into half circles.
Melt butter in a large stock pot over low heat and add onions. Cook, stirring occasionally until onions are very soft and starting to get dark, up to 60 minutes.
Increase heat slightly and add sugar. Continue to cook, stirring frequently until onions turn dark golden brown and begin to caramelize, being careful not to let them burn,
Add white wine and cook over medium heat for a few minutes, stirring up the brown bits. Add chicken broth, bay leaf, Worcestershire sauce, thyme, salt and pepper. Simmer for 20-30 minutes on low.
Meanwhile, arrange baguette slices on a baking sheet. Toast under broiler until lightly toasted, then turn and toast other side. Or grill. Remove from oven and rub garlic briskly over each piece while still warm.
Preheat oven to 400 degrees on convection roast setting so heat is coming from the top.
Remove bay leaf and thyme sprigs from soup and ladle into 4 oven safe bowls. Top with two toasted baguette slices, pressing gently into the broth. Top with sliced cheese, arranging so top is covered and some hangs over the bowl edge.
Roast for about 10-15 minutes until cheese is melted and bubbling on top. Use broiler at the end if necessary to slightly brown the cheese.
Allow to cool slightly before serving.