How to Make It
Remove shells from middle part (where legs attach) of 12 shrimp, keeping heads and tails attached. Reserve shells. Devein shrimp, and set aside.
Remove shells from middle part of remaining shrimp; remove heads, leaving tails attached. Reserve shells and heads. Devein shrimp. Arrange all shrimp in a single layer on a parchment paper–lined baking sheet. Sprinkle both sides of shrimp evenly with 1 teaspoon salt. Cover with plastic wrap, and place in refrigerator.
Combine 10 cups water, onion, bay leaf, 2 garlic cloves, and reserved shrimp shells and heads (about 3 cups) in a large stockpot. Bring to a boil over high; reduce heat to medium, and simmer until mixture has a light shrimp flavor, about 20 minutes. Pour through a fine wire-mesh strainer into a large bowl, pressing on solids to extract all liquid. Discard solids. Set stock aside.
Combine tortilla pieces, tomatoes, chipotle chiles, and remaining 2 garlic cloves in a blender. Process until slightly smooth, about 40 seconds.
Add 2 tablespoons grapeseed oil to stockpot. Heat over medium until oil is very hot. Pour tomato mixture through a fine wire-mesh strainer into stockpot; discard solids. Cook, stirring often, until thickened, about 10 minutes. Whisk in shrimp stock; increase heat to high, and bring to a boil. Reduce heat to medium, and simmer, whisking occasionally, until flavors have melded, about 20 minutes. Season to taste with salt and pepper.
Meanwhile, knead together masa, peanut oil, and remaining 1 teaspoon salt in a medium bowl until oil is absorbed and mixture is no longer crumbly. Divide dough into 20 (about 1/2-ounce) portions; shape each portion into a 1 1/4-inch ball. Press your finger into each ball to make an indentation in dough. Arrange dumplings in a single layer on a baking sheet.
After stew has simmered 20 minutes, gently drop dough balls into stew. Cook, maintaining a simmer and stirring occasionally, until dumplings have the texture of cooked tamales, about 30 minutes. Remove from heat; gently stir in shrimp, and allow residual heat to cook shrimp, stirring occasionally, until no longer pink, about 10 minutes. Season with salt and pepper.
Pat scallops dry with a paper towel, and season with salt and pepper. Heat remaining 2 tablespoons grapeseed oil in a medium skillet over medium-high until shimmering; swirl to coat. Add scallops; press lightly with a spatula, and cook, undisturbed, until golden brown around edges, about 3 minutes. Flip and cook, undisturbed, 30 seconds. Transfer to a plate lined with paper towels; set aside.
To serve, use a slotted spoon to divide shrimp and dumplings among bowls. Ladle broth into bowls, and top with scallops. Garnish with parsley, and serve with lime wedges.
If you can’t find head-on shrimp, start recipe at Step 4 using 1 pound peeled and deveined raw shrimp and 8 cups best-quality chicken broth. To make chochoyotes using corn masa flour instead of fresh masa, mix 1 cup masa flour, 3/4 cup water, 1 tablespoons peanut oil, and 1 teaspoons kosher salt in a medium bowl until smooth. Decrease cooking time for the dumplings to 20 minutes.