In a griddle, melt ½ stick of butter with 1 tbsp of grapeseed oil over low heat. Add thinly sliced onions and sauté until they become soft and translucent. Add 3 sprigs of thyme, garlic, and tomato paste. Continue to sauté until the onions begin to caramelize.
While the onions are cooking, place a small pot on the griddle over low heat. Add vegetable broth, not-beef bouillon, and Worcestershire sauce. Stir to combine.
Once the onions have caramelized, remove the thyme sprigs and discard them. Add the caramelized onions to the broth, place the lid on the pot, and allow the mixture to simmer for 10 minutes.
While the soup is simmering, add additional butter to the griddle and toast the bread slices on both sides.
Ladle the soup into your bowl and top it with the toasted bread slices.
While the griddle is still on low heat, place each slice of provolone cheese on it. Once the cheese begins to melt, remove each slice with your spatula and lay it over the toasted bread.
