1/2 gallon cream (preferably without additives)
1/2 c buttermilk
1 tsp kosher or sea salt (optional)
Pour cream and buttermilk into a large bowl, stirring to combine. (I just put it into the bowl of my mixer.) Cover and leave on the counter at room temperature for 24 hours.
The next day, thick creme fraiche (real sour cream) will have formed. This stuff is awesome as is! Using a butter churn, stand or hand mixer, whip the cream until it starts to look grainy. If using a mixer, keep an eye on the cream because when the emulsion breaks, the liquid can go everywhere. Once the butter starts blobbing up in the bowl and liquid buttermilk separates, beat until there is no more cream visible.
Strain the mixture through a fine sieve into a bowl to catch the buttermilk. Gently press on the butter solids to release the liquid. Reserve the resulting buttermilk for awesome pancakes (yes, everything goes into pancakes.) Further rinse the butter with cold running water.
Next step is to literally squeeze the butter to release any remaining buttermilk. I use my hands, but you could also use two butter paddles, traditionally used exactly for this purpose. The more buttermilk you remove, the richer your butter and the longer it will last. Don’t do this to long or the heat from your hands will melt the butter. If you want to salt your butter, now is the time. Sprinkle with 1 tsp salt and knead into the butter. I prefer mine unsalted.
Form the butter into blocks or logs and wrap with waxed paper or plastic wrap. To protect it from picking up off-flavors in the fridge, I also place the butter in plastic zipper bags.
Recipe will make about 1.5-2 pounds of butter.