Make soup. Melt 1 tablespoon of butter in a large pot over medium heat. Add onion cook until beginning to soften, 2 to 3 minutes. Stir in garlic and cook until fragrant, about 30 seconds. Add tomatoes, stock, 1 teaspoon salt, and 1/2 teaspoon black pepper. Bring to a boil and simmer 15 minutes. Stir in cream and garnish with fresh basil.