Step 1Place the shrimp in a saucepan with enough cold water to cover by ½-inch. Bring the water to a boil over high heat, then remove from heat and set aside until the shrimp are fully cooked through (they will be opaque and firm to the touch), about 5 minutes.
Step 2Drain the shrimp, saving the liquid, and cover them with ice just until they are cool, then quickly remove the ice so the shrimp don’t lose any flavor. Remove and save the shells.
Step 3Place the shells and cooling liquid in a food processor and very finely grind the shells until the liquid is foamy and takes on the color of the pink shells, about 5 minutes. Place the mixture in a saucepan and gently simmer for 10 minutes to infuse the liquid with the flavor from the shells. Remove from heat and strain the shells, saving the liquid. Keep the liquid warm.
Step 4In a bowl, combine the tomatoes, onion, chiles and cilantro, sprinkling over the lime juice and mescal. Gently stir together and taste, adding ¼ teaspoon salt, or as needed.
Step 5Coarsely chop the shrimp and add them to the warm liquid, then spoon the mixture into 4 large wine glasses. Add the salsa mix, and serve with lime wedges and a bottle of your favorite hot sauce.