4lbJapanese sweet potatoes peeled and cut in quarters
1stickbutter plus 3 tbsp for garnish
Place the peeled and quartered sweet potatoes into a large pot. Pour the chicken stock over the potatoes and then add enough water to cover. Add two big pinches of salt and bring to a simmer. Cook the potatoes until they are fork-tender, about 20 minutes. Reserve one cup of the cooking liquid then drain through a colander.
Rinse out the pot the potatoes were cooking in and place it back on the stove over low heat, and add in the cream and butter. Position a potato ricer or food mill over the pot and pass the cooked sweet potatoes through the mill and into the cream and butter mixture. Use a large spatula to fold the butter and cream into the riced potatoes. Season generously to taste with kosher salt. Transfer the potatoes to a bowl and top with a few slices of butter. Serve immediately.
Use the reserved potato cooking liquid as needed to loosen up the potatoes if they become too thick.