To remove the air from a freezer bag with a slider closing, hold the bag open at the top while slowly lowering it into the water. The pressure of the water will squeeze the air out of the bag. Just before the top of the bag reaches the water, zip it closed.
Do not submerge the seal of the bag. Clip the top of the bag to the side of the pot ensuring the seal will not go underwater to prevent liquid from leaking into the bag. It is important to ensure the food is fully submerged in water throughout cooking. If the food bag floats above the water, use a heavy, heat-resistant utensil, a plate or RICARDO magnetic weights to hold the bag down and keep the food submerged.
To cook the cod in a skillet
In a large non-stick skillet over medium-high heat, cook the cod pieces in the butter for 3 minutes or until nicely browned on one side. Season with salt and pepper. Flip the fish over and continue to cook over medium heat for 2 to 3 minutes or until the fish is cooked through.