This recipe works best with a combination of clarified butter, which you can buy in large supermarkets as Indian ghee, as well as regular unsalted butter. Or, you can clarify butter yourself; my colleague David Lebovitz has a tutorial here. You use the clarified butter to cook the frog legs and the regular butter for the sauce. Why bother? Clarified butter has a higher smoke point and holds up better when frying the frogs, while the regular butter tastes creamier for the sauce. You can of course use regular butter for everything, but it will scorch a bit.
I served my frog legs with sauteed chanterelles and crusty bread. But boiled or roasted fingerling potatoes would be another good option, green beans an ideal veggie, or maybe a bitter greens salad with a vinaigrette dressing. White wine or a lighter beer, i.e., a lager or pilsner, is a must.