Pour a cup or two of heavy cream in the blender. Add a tspn or so of salt, and blend it on med. it’ll turn to whipped cream and then chunk into butter. Let it run for a minute or two more as the liquid co to yes to separate from the butter.
Scoop the butter into a non fuzzy towel or a few layers of cheesecloth and squeeze the remaining liquid out. Spread on hot bread or grab a spoon.