In a large soup pot, melt
the butter over medium-high heat. Add the onion
, and garlic and cook until the vegetables are tender, about 4 minutes. Add the beans
, tomatoes, broth, bay leaf
, 1 teaspoon rosemary, and red pepper flakes. Bring the soup to a boil over high heat, then reduce the heat to low and simmer
for 30 minutes, covered.
Puree the soup
in a blender
in batches, being careful to remove and discard the bay leaf. Return the soup to a soup pot and keep warm over low heat. Season with salt and pepper.
In a medium bowl fold in the lemon zest
and the remaining teaspoon of rosemary to 2/3 cup creme fraiche. To serve, ladle the soup into bowls and dollop
each bowl with the lemon rosemary creme fraiche. Serve immediately.