In a medium pot, heat the oil. Add the onion and cook over medium heat, stirring frequently, until tender and lightly browned on the edges, about 7 minutes. Add the garlic and thyme; stir until fragrant, about 1 min. Add the tomatoes, broth, honey, salt, and pepper. Bring to a boil over high heat. Reduce the heat and simmer, stirring frequently, until reduced by a quarter and thickened, about 15 minutes. Using a stand or immersion blender, puree about half the soup; it will be still be chunky and thick. Return it to the pot and stir in the cream. Heat gently and adjust the seasonings. Ladle into bowls, sprinkle with the parsley if using, and serve immediately.

Arrange an oven rack to the highest rung and heat the broiler on high. Line a baking sheet with foil. Put the bread on the foil and toast each side until golden brown. Spread the mustard evenly on one side of each toast, cover with the Gruyere, and sprinkle with the Parmesan. Slide the toasts back under the broiler and cook until bubbling and lightly browned on top, about 2 minutes. Cut each toast in half and serve immediately with the soup.