Heat a sous vide water bath to 190°F (88°C) degrees. Make sure the potatoes are scrubbed clean.
Use a fork to puncture small holes in each side of the potatoes in multiple places (like you would to microwave them).
Place the potatoes in a vacuum seal bag with the butter, salt and pepper.
Seal and cook for 2 hours. Will likely float so may need to weigh down to keep the bag submerged.
Remove from the water bath and serve immediately with topping, or place under the broiler/cat iron skillet/torch/grill to crisp the skin then serve with toppings.
If broiling, rub an additional teaspoon of oil or melted butter on the outside and coat it with salt to get a nice crispy, salty skin.
**can also place in an ice bath for 20 minutes then kept in the fridge for 3-5 days before serving.
Notes
If the bag starts to float, weigh it down with something heavy or try these sous vide magnets or sous vide weight. The bag needs to be submerged so the potatoes cook evenly.
If broiling/searing/torching the potato to crisp the skin, make sure the skin has been thoroughly dried so you can achieve the crispness.
You can replace the butter with olive oil, bacon fat, duck fat or any other fat you prefer.
To make in advance, place them in an ice bath for 20-30 minutes when they come out of the water bath (directly in the bags). Then store in the fridge or freezer until ready to use. Reheat at 190°F for 15-30 minutes (depending on whether frozen or not).