In a large saucepan, heat 1/4 cup butter until melted. Add sliced onions. Cook until tender, but not brown.
Add tomatoes to saucepan.
Stir in tomato paste, basil, thyme, salt, and hot sauce.
Stir in broth.
Bring to a boil; reduce heat. Cover and simmer for 30-40 minutes.
Place in blender (1/2 of the quantity at a time). Strain to remove any seeds.
Return to saucepan. Heat through.