Preheat the broiler and line a baking sheet with foil. Soak the shallots in ice water for 5 minutes, then drain and set aside.
Put the tomatillos cut-side down on the baking sheet. Broil until soft and charred in spots, rotating the baking sheet as needed, 4 to 5 minutes. Let cool.
Transfer half of the tomatillos to a blender along with the 1/4 cup packed cilantro leaves and stems, lime juice and salt. Blend until smooth. Remove the skins from the remaining tomatillos and cut into small chunks.
Toss the tomatillo sauce, chopped tomatillos, scallops and drained shallots in a medium bowl. Cover and refrigerate until the scallops are opaque and firm, tossing a few times, at least 30 minutes and up to overnight.
Toss with the chopped cilantro before serving. Serve with corn tortillas, if using.
From Food Network Kitchens