Prepare the potatoes by scrubbing them clean and peeling them. Dice into ½ inch cubes. Set aside in a large bowl with enough water to cover. This will prevent oxidation.
Cut the bacon into ½ in x ½ in pieces, and place into the cold basin of your Instant Pot.
Press the Sauté button, and set for 15 minutes. Stir every 3 minutes. Fond will begin to form on the bottom of the pan.
Drain and remove the bacon. You may optionally filter and reserve the bacon fat for future cooking. Keep in the refrigerator. DO NOT POUR BACON GREASE INTO YOUR SINK.
Mince the onion and add to the pot, setting once more to Sauté for 10 minutes. Use the liquid released from the onion to scrape up the browned bits at the bottom of the pan. Once deeply brown, but not burned, add in garlic. Turn off Sauté function, and remove the onions to the same reserving bowl as the bacon bits. New fond should have collected at the bottom of the pot again.
Deglaze the pot with the heat OFF with the white wine. Scrape the bottom of the pot clean. The wine should turn dark golden brown.
Drain the starchy water off of the potatoes, and add them to the Instant Pot along with the bacon and onions. Toss them in the wine sauce.
Add enough clean water until the potatoes are just covered, and season with salt.
Seal the Instant Pot lid in place, and turn on the pressure cook function for 5 minutes. Allow to depressurize naturally.
Using the back of a serving spoon, mash about half of the potatoes for a chunkier soup. You can mash more for a smoother texture.
Stir in ½ cup of milk and ¾ cup of cheddar cheese.
Serve with a dollop of sour cream and a sprinkling of green onion as desired.