2 cups heavy or whipping cream, chilled
Pour the chilled cream into the bowl of a stand mixer fitted with the paddle attachment. Beat the cream on medium speed until it starts to thicken and form whipped cream, 2 to 3 minutes. Stop the mixer.
Drape a large, clean dish towel over the top of the mixer so it hangs down around the outside of the bowl, but not inside it (the towel will contain the splashes and drips in the next step).
Beat the whipped cream on medium-high speed until it separates into liquid buttermilk and solid butter, 8 to 10 minutes (you’ll hear the buttermilk start to slosh around when it happens!). Stop the mixer.
Move the towel out of the way to see if the yellow chunks of butter look solid and are clinging to the paddle and the liquid buttermilk has pooled at the bottom of the bowl; if not, re-cover and keep beating for another 1 to 2 minutes until they do.
Set a fine-mesh strainer over a medium bowl. Use a rubber spatula to scrape the butter off of the paddle and into the mixer bowl. Scrape the butter and buttermilk mixture into the strainer, catching the solids. Use the spatula to gently press out as much liquid as possible from the butter solids into the bowl. (You can use the buttermilk in another recipe or discard it.)
Hold the strainer with the butter in it under cold running water in the sink. Gently press and knead the butter with your hands or the rubber spatula until the water runs clear.
¼ teaspoon table salt
Transfer the butter to a small bowl. Sprinkle with the salt, then press and mix with the rubber spatula until it’s evenly incorporated and the butter is smooth. If any liquid pools on the bottom, drain it off into the sink. Serve (especially on hot toast!), or transfer the butter to an airtight container and refrigerate for up to 2 weeks.