How to Make It
Heat oil in a Dutch oven over medium-high. Add onions; sauté 10 minutes or until tender. Reduce heat to medium-low. Stir in thyme, salt, and pepper; cook 40 minutes or until golden-brown, stirring occasionally.
Increase heat to medium-high. Add vermouth, scraping pan to loosen browned bits. Cook until liquid almost evaporates. Stir in stocks; bring to a simmer. Stir in Marmite; cook 5 minutes or until Marmite dissolves.
Preheat broiler to high with rack in top position. Place bread on broiler pan; top each slice with 2 tablespoons cheese. Broil 3 minutes or until cheese bubbles and browns in spots. Ladle 1 cup soup into each of 8 bowls; top each with 1 cheese toast, and garnish with thyme.