Wash potatoes (scrub any dirt off) and rinse. Peeling isn't necessary but if you prefer that, go ahead.
Pressure Cook Method: Place whole potatoes directly in pressure cooker pot without trivet. Pressure cook on high for 11-12 minutes, let naturally release for 10 minutes. Drain water - reserve about a half cup of the cooking water in case you need it for mashing.
Boil Method: Quarter potatoes and place in a large cooking pot, put in enough water to submerge all the potatoes. Boil until soft (test with a fork). Drain water - reserve about a half cup of the cooking water in case you need it for mashing.
Add optional spices if you want some extra flavor. These are good with our without so this is totally optional. Most of the time I make mine plain.
Mash with a hand masher until mostly smooth. Use a smidgen of the cooking water if it helps you mash easier. You want to keep the liquid minimal. It's okay if there are some small chunks.
Transfer mash potatoes into a square or rectangular food storage container. Firmly press into container. Let cool to room temperature without lid.
One cooled you can store in the fridge overnight with the lid on.