Prepare your water bath and immersion circulator set to 190°F. Make sure you’ve placed your water bath on an appropriate heatproof surface.
Scrub your potatoes with a brush under water and remove any serious blemishes or eyes.
Place potatoes and other ingredients in a vacuum bag and generally try to evenly disperse ingredients. I’m pretty much 100% sure this doesn’t matter, but it makes me feel better.
Lay bag flat on its side so that the potatoes form one even layer and vacuum seal.
Place potatoes into the water bath and cook for 1 to 2 hours depending on the side of the potato (1 for ping pong ball sized potatoes, 2 for racquet ball-sized potatoes). Take appropriate steps to keep potatoes from floating.
Once the appropriate time has elapsed, carefully remove your bag from the water bath. Place the bag on a towel and gently smash the potatoes with a hard flat service. I generally use a rocks glass, or the bottom of a cast-iron skillet. You only need to do this enough to break the skin and flatten them some, they’re smashed not mashed.
Carefully remove smashed potatoes from the bag keeping them intact if possible and place them on a plate or cutting board.
Prepare an oiled cast-iron skillet or flat top on medium-high heat and place the potatoes in to cover the bottom. No worries about crowding here, get as many in as you’ll be able to maneuver and flip.
Cook potatoes until the skin and exposed flesh has browned and crisped and flip. About 3 minutes.
Allow the second side to cook for a minute or so then reduce heat and top with a good melting cheese such as mozzarella.
Allow cheese to melt, with the assistance of a lid if available, and scoop potatoes and melted cheese onto a serving platter. Be sure to get those crispy bits of browned cheese!
Repeat with remaining potatoes, if any.