If using fresh shrimp, peel and devein. In a medium pot, add ½ lemon, and optional bay leaves and peppercorns. Add enough water to cover shrimp. Bring water to a boil. Drop shrimp in and cook for 2-3 minutes or until just pink. When done, drain shrimp and place in a bowl with ice and water to shock the shrimp. (Shocking stops the cooking process.) When shrimp are chilled, drain and set aside.