Rock Shrimp Cocktail with Avocado

1. In a small bowl, combine the sour cream, onion, and salt to taste. Cover and refrigerate. In another small bowl, combine the ketchup and horseradish. Cover and refrigerate.
2. Fill a large saucepan with water and add the peppercorns and bay leaf. Bring to a simmer over medium-high heat. Add the shrimp and cook for 2-3 minutes until they begin to curl. Remove the shrimp with a slotted spoon and run under cold water to cool quickly. Set aside.
3. Juice half the lime in a small bowl. Cut the other half into wedges and set aside. Halve and pit the avocado. Scoop the flesh into the bowl with the lime juice. Add the cumin, salt, and pepper to taste. Mash with a fork.
4. Divide the avocado mix evenly among 4 martini glasses or other attractive 8-ounce glasses. Top each one with 1/4 of the shrimp. Spoon a few tablespoons of the sour cream mix on top. Finish with a small spoonful of the horseradish sauce and wedge of lime.