Place the macaroni, chicken stock, cream, salt and pepper into the pressure cooker.
Bring the pressure cooker to high pressure, then adjust heat level to stay at high pressure. Cook for 7 minutes.
Remove from heat. Follow recommendations for your pressure cooker on how to let the steam out of the pressure cooker. (For my electric pressure cooker, I have to wait 10-15 minutes before releasing steam.).
Remove the lid, directing the steam away from you.
Add the butter, milk and cheeses to the pot and stir.
Note: If you have no heavy cream, melt 1/3 cup butter in the microwave and then add 2/3 cup milk. If you have 2% milk, add a tablespoon of flour to the ingredients.