Fill the Ninja Foodi Inner pot with 10 cups of water or your sous vide container with enough water that the shrimp can be fully submerged during the cooking process.
Set the sous vide circulator temperature to 140°F/60°C and allow the water to heat up. If using the Ninja Foodi, put the pressure lid on and turn the valve to vent. Select the sous vide function and set the temperature to 140°F/60°C
Peel and devein the shrimp, leaving the tail on. Lightly toss in salt. Place butter into the bag and lay the shrimp in the bag in a single layer and slightly curled. Seal the bag using a vacuum sealer or the water displacement method.
When the water is heated to the correct temperature, lower the bag into the water and sous vide cook for 15 minutes. If the bag is floating, use a bowl or a plate to weigh it down. The shrimp need to be completely submerged in the water.
When the time is up, remove the bag and open it. Remove the shrimp and place on a plate. Put the plate in the fridge to cool for 30-60 minutes. If storing longer, make sure the shrimp are in an airtight container so they don't dry out.
When chilled, serve with cocktail sauce and lemon wedges.
Homemade Cocktail Sauce
Combine the ketchup, Worcestershire sauce, horseradish and lemon in a small bowl and mix to combine. Cover and refrigerate until serving.