Drain clams, reserving the liquid.
Heat the cooker using the SAUTÉ function. Add the diced bacon and sauté until it is crisp. Remove the bacon, leaving the fat in the cooker and set aside.
Add the onions and the celery to the hot bacon fat in the cooker, and cook, stirring, until softened, about 3 minutes. Add the clam juice, potatoes, salt, pepper, and bay leaf. Stir to mix and lock the lid in place.
Set the regulator knob to PRESSURE. Set the cooker to Pressure Cook on HIGH for 5 minutes and press START.
When done, use the natural release method to depressurize the cooker. Carefully open the lid after pressure drops. Discard the bay leaf and add the milk, half and half, and the crumbled bacon.
Use the SIMMER function to simmer for 2 minutes. Do not allow the soup to boil. Add the clams and continue stirring for 1-2 minutes until the clams are warmed through. Serve immediately.