Recipe Notes
Using the buttermilk: The buttermilk and rinse water can be used in bread and other baked goods or to make smoothies.
Cultured butter: Cultured butter will last longer and has a more complex flavor than regular milk. To make cultured butter (and buttermilk), mix two tablespoons of plain yogurt, kefir, or other fermented dairy with live cultures into the cream. Cover and let sit at room temperature overnight, or about 10 hours. The cream is "cultured" when it has thickened slightly, smells tangy and sour, and is a little foamy. Use the cultured cream right away or chill until ready to use. Read more about it here: How To Make Cultured Butter.
Food-processor butter: You can also make butter in a food processor. Follow the directions as written; it may take slightly longer for the butter to separate.