Pressure Cooker Mashed Potatoes

2 pounds russet potatoes, peeled and halved
1/2 cup milk
4 tablespoons unsalted butter
Salt and pepper

Place 1 cup water in the pressure cooker and add the rack. Stack the halved and peeled potatoes on the rack. Seal the lid and set to high pressure for 15 minutes. Quick release the pressure and drain the potatoes. Remove the rack. Add the potatoes back to the pot and add the milk, butter, and salt and pepper to taste. Mash with a potato masher to desired consistency. Serve.