Scrub potatoes well to remove any dirt, then peel (unless you are using a food mill to process, in which case you do not need to peel your potatoes). Cut potatoes into quarters or eighths, depending on the size. You want approximately 1-inch size pieces (all fairly even in size so they will cook uniformly) and transfer to a bowl filled with cold salted water. You can prep and cut your potatoes a few hours ahead of time if necessary; keep covered in water to prevent browning.
Boil potatoes in a large pot of generously salted water for about 15 minutes or until fork tender (a fork inserted into a piece of potato should go in easily and the potato should somewhat break apart). Drain well.
Run potatoes through a food mill placed on top of your still warm cooking pot on the still warm burner. The residual heat from the pot will evaporate out any excess moisture from the potatoes. If you don’t have a food mill, run potatoes through a potato ricer, or place in the pot and mash with a potato masher until smooth.
Add butter and stir until melted, then add heavy cream and sesame oil. Season generously with salt and pepper.
Serve warm, topped with a sprinkle of toasted sesame seeds if desired.