1 1/4 pounds large shell-on shrimp preferably head-on
1/2 cup mild Mexican hot sauce
1 tablespoon fresh lime juice
1 teaspoon Maggi liquid seasoning or soy sauce
1 teaspoon Tajín Clásico seasoning or kosher salt and freshly ground pepper
1/2 cup chilled unsalted butter cut into pieces, 1 stick
1 cup thinly sliced red onion
Cook shrimp in a large pot of boiling salted water just until opaque, about 30 seconds. Transfer to a paper towel–lined baking sheet and let drain.
Bring hot sauce, lime juice, Maggi seasoning, and Tajín seasoning to a gentle simmer in a large skillet over medium-low. Whisking constantly, gradually add butter a few pieces at a time. Whisk until all butter is incorporated and sauce is emulsified.
Add shrimp and cook, tossing gently and adjusting heat as needed to keep sauce just below a simmer, until cooked through, about 5 minutes.