When a potato cooks, the starches contained in each cell are released as the cell walls break down. These starches absorb the potato’s internal moisture and swell and soften. These two processes are what transform a raw, hard potato into a cooked, softer potato fit for mashing.
If you cut your potatoes up before boiling them, the starches absorb the internal potato moisture as well as the water in which they’re being boiled. If they boil for too long, they absorb too much water and your mashed potatoes will become gummy. The difference between perfectly cooked potato pieces and soggy pieces can sometimes be as little as a minute or two.
An easy workaround is to boil potatoes whole. They’ll take a bit longer to cook but you can leave them in the hot water after boiling without undesirable effects, keeping them warm until it’s time to mash them. I start my potatoes boiling as soon as I begin cooking and mash them immediately before dinner.
If they need more moisture, you can add a bit of hot potato boiling water or another liquid. This way, you have more control of their moisture content.
Mostly it’s about using room temp water in the pot.
If you use hot water, thinking they will cook faster, that’s the step that will make them gluey for sure.
So start them off in room temp water.
I prefer unpeeled Red Bliss 🥔 myself.
I simmer some milk or cream and butter with some roasted garlic for the real goodness.
Bigger potatoes, chunk em into quarter size.
Definitely peel starchy potatoes.
Waxy ones like Red Bliss or Golden/New Potatoes, I leave the skin on for nutrients/nutrition.
And don’t let them sit in the water after for too long, at least drain them first if you aren’t gonna mash right away before serving.