Heavy whipping cream (not milk, and not half and half)
Dash of salt (optional)
Yellow food coloring (optional)
How to do it:
Fill the small jar 1/4 to 1/2 way full of (unwhipped) whipping cream/heavy cream. Cream should be cool. Replace the lid tightly.
Start shaking! You will need to shake the jars for about ten to fifteen minutes before the butter starts to separate. You can hear it starting to happen as you shake, because it will feel like you’re shaking a lump of something. This is the curd separating from the whey. Shake until the remaining liquid (whey) is watery and translucent.
Use a strainer to drain off the whey. If you plan to keep your butter and don’t use it all immediately, it is important that you wash out all the whey to help the butter last. You will need to ply it (mash it) with a spoon and rinse until the water is clear.
Next, rinse the lump of butter with cool water two or three times, or until the water runs off clear. (If the weather is warm, you may need to chill the butter before rinsing.) It will look sort of like scrambled egg.
If you’d like to add salt, do it now. And with or without salt, you will want to knead the butter a bit to help consolidate it. When you’re all done, you can pack them into cube shapes, or leave as-is. (Of course, your butter will probably not look much like the packaged sticks from the grocery store, and may be almost white in color.)