In large Dutch oven or stockpot over medium heat, melt butter. Add onion and cook, stirring occasionally, 8 to 10 minutes until onion is softened and lightly browned. Add a generous pinch of salt and a dash of pepper. Add tomato paste and stir into onions. Cook 2 minutes, stirring constantly until tomato paste is darkened in color. Add crushed tomatoes, broth, thyme, bay leaf and sugar. Bring to simmer; add more salt and pepper to taste.

Simmer uncovered 35 to 40 minutes, stirring occasionally, until flavors meld and soup thickens ever so slightly. Remove from heat; stir in cream. Remove thyme and bay leaf. Use immersion blender (or regular high-speed blender, in batches) to blend soup until smooth.

Serve with gooey, buttery grilled cheese sandwiches cut into soldiers for maximum dipping ability.