Pour the cream into a large bowl or the bowl of your stand mixer. Beat the cream on medium-high speed until it thickens into whipped cream.
2 cups whipping cream
Reduce the speed to medium-low and continue to beat the cream until it separates and the butter sticks to the beaters. You may want to cover the bowl during this step to prevent splatters.
Set a fine-mesh sieve over a bowl and carefully pour the liquid through it.
Put the butter in a clean bowl and pour COLD water over it. Use your hands or a spatula to knead the butter to clean any remaining buttermilk. Drain the water and repeat until it runs clear.
If you're using salt, put the butter on a plate, sprinkle salt over the top, then mix it into the butter.
½ teaspoon sea salt
Store the butter in your fridge, either wrapped in waxed paper or in a jar, for up to 2 weeks.
Notes
Can I make homemade butter last longer?The key to making homemade butter last longer is to rinse it well under cold water—the cream spoils, not the fat. But the cream also makes the butter taste amazing, so you'll need to decide what is most important to you: flavor or storage.