Preheat the oven to 425 degrees.
Wash, quarter and remove stems from the tomatoes.
Slice the onion into wedges and peel the garlic.
Place the vegetables on a baking tray (lined with foil for easy clean up), and toss them with the olive oil, vinegar and salt to coat. Place the tray in the oven and bake for 30 minutes.
Place the vegetable stock and thyme in a large pan and simmer over low heat while the tomatoes are roasting.
Once the tomatoes are done, add them to the stock.
Add the chopped basil and sugar. Let it simmer for about 5 minutes.
Remove the thyme stems before blending the soup!
Remove from the heat and use an immersion blender, cream the soup.
Add in the heavy cream and return the pan to simmer for about 10 minutes for the flavors to blend.
While the soup is simmering, make the grilled cheese.
Coat the outside slice of the bread with butter and add about ¼ c of each type of cheese on top of the bottom slice.
Stack the top slice with the butter side up and grill on each side until the bread is golden brown.
Remove and serve alongside the soup.