Prepare the shrimp: Combine 8 cups cold water, 2 tablespoons salt, the coriander and peppercorns in a large saucepan. Squeeze in the lemon juice and add the wedges. Boil 5 minutes, then remove from the heat, add the shrimp, cover and set aside, about 15 minutes. Strain and transfer the shrimp to a bowl; cover and chill at least 1 hour.
Meanwhile, make the sauce: Preheat the oven to 350 degrees F. Place the tomatillos, onion, garlic and jalapenos in a roasting pan. Toss with the canola oil and season with salt and pepper. Roast until soft, tossing occasionally, 25 to 35 minutes.
Cook the spinach in a saucepan of boiling water, about 1 minute. Drain, squeeze dry and transfer to a food processor. Add the tomatillo mixture, vinegar, horseradish, cilantro and honey and pulse until smooth; season with salt and pepper. Transfer to a bowl, cover and chill at least 1 hour. Bring to room temperature 15 minutes before serving. Serve the sauce and shrimp in shot glasses, if desired.
Photograph by Mark Peterson
Recipe courtesy of Bobby Flay for Food Network Magazine