Triple Grilled Cheese with Tomato Soup

This was in one of my Food Network Magazines.  This will become a lunch staple as the weather gets cooler, I am sure.

1/4 C. extra virgin olive oil
1 medium onion, finely chopped
1 clove garlic, chopped
1 small stalk celery, chopped
2lbs tomatoes, chopped
1/2 tsp. sugar
Kosher salt and ground pepper
1 C. shredded muenster cheese
1 C. shredded part skim mozzarella
1/2 C. grated Parmasan cheese
8 slices thick sandwich bread
2 to 3 tbsp. unsalted butter, softened

Combine the olive oil, onion, garlic, celery, tomatoes, sugar and 1 tsp. salt in a saucepan.  Cook over medium heat, stirring occasionally, until vegetables are tender, about 25 minutes.  Puree until smooth with an immersion blender, or transfer to a regular blender and puree.  Season with salt and pepper and keep warm.  Add water to thin soup if desired.

Meanwhile, combine all three cheeses in a bowl.  Divide evenly between 4 bread slices and top with remaining bread.  Heat 1 tbsp. of butter in a large skillet over medium heat.  Cook the sandwiches in batches, adding the remaining butter as needed until the cheese melts and the bread is golden, 3 to 4 minutes per side.  Serve the sandwiches with the soup.