Melt the butter in a pot, add the onion, celery, carrot, and garlic. Cook until onion and celery is tender. Add flour (you're making a roux), stir, and cook for a little longer. Add tomato paste, broth, and nutmeg. Cook until vegetables are completely soft. Use a stick blender in the pot to pureé the soup and add cream, salt, and pepper.

Creme fraiche makes a wonderful garnish with some basil. You can also add other vegetables when you add the tomatos. Zucchini is nice, as is spinach.