This simple lentil salad has a little secret: a toasty, brown butter vinaigrette perfumed with sage. The dish has as much texture as it does flavor. French green lentils or black lentils are the ideal choice, as they hold their shape well after cooking, but brown lentils will work too, though they’ll be a bit softer. Start testing your lentils for doneness after about 15 minutes of cooking; you want them cooked through but not mushy, and they’re best if they retain some bite. Roasted until…