Roast tomatillos until soft.
Place tomatillos in a blender with the remaining dressing ingredients and blend
until smooth.
Transfer to a bowl, taste, and adjust the salt. Set aside.
Roast or steam the corn kernels above ½ inch of boiling water for 5 to 7
minutes, until tender. Remove from the heat and refresh with cold water.
Roast or steam the potatoes until crisp-tender, about 10 minutes.
Remove from the heat and toss with the corn.
Bring a small pot of water to a boil and drop in the fava beans. Boil for 1
minute and immediately transfer to a bowl of cold water.
Pop off the shells and toss with the corn, potatoes, and remaining salad
ingredients, except lettuce, in a bowl.
If the dressing is quite thick, thin out with a couple of tablespoons of water.
Toss with the salad. Allow to cool and chill if desired. Taste and adjust the
seasonings.
Serve with fresh greens.