Fill the pressure cooker with 1 cup of water. Place the steamer trivet in the pot and add quartered potatoes in the steamer trivet. Close the lid. Cook on Manual at high pressure for 8 minutes, then quick release. While the potatoes are cooking, heat a small sauce pan over medium heat. Melt the butter and add the garlic. Add a pinch of kosher salt. Sauté the garlic for 1 to 2 minutes until fragrant and golden in color. Add the milk and deglaze the pan. Remove mixture from heat when it is hot. Remove the lid. Mash the cooked potatoes in a medium mixing bowl with a potato masher. Don't mash the potatoes too aggressively, as that will make the mashed potatoes gluey and unappetizing. So be careful if you're using a food processor to mash the potatoes. Add half of the garlic butter mixture to the bowl. Continue to mash, stir, and add the mixture until desired consistency. Add Parmesan cheese. Taste and season with salt and pepper. Serve warm and enjoy!! You may use unpeeled potatoes if you prefer. If you want fluffy mashed potatoes, use starchy potatoes like Russets or Yukon Golds. Don't substitute it with other types of potatoes.