The combination of lamb and white beans is not exclusively French, but this particular version is from Brittany. The lemon-thyme butter will keep well in the refrigerator for 2 to 3 days.
For the butter, heat 2tablespoons butter in a small sauté pan over medium heat. Add the shallots and cook until tender. Add the thyme and cook 2 minutes more; let cool 10 minutes. Place the onion mixture, lemon juice and zest, and remaining butter in a food processor and process until blended. Seas