Fun fact: Cultured butter produces two delicious byproducts: buttermilk and fresh sour cream (also known as crème fraiche)!
1. Place your quart jar filled with cream into a large pot filled with hot tap water.
2. Sprinkle a scant 1/8 teaspoon of Flora Danica on to the surface of the cream. Let it sit on top of the cream for about 5 minutes to rehydrate, then stir for a minute.
3. Cover the pot with a clean dishtowel and let sit for 8 to 12 hours. After the first 4 hours, refresh the water bath with another round of hot tap water.
4. When the cream has cultured, it will have thickened and will smell quite tangy. Scoop off the thickest layer on top and save it for later—that’s crème fresh (also known as fresh sour cream).
5. Check the temperature of the cream. You’re aiming for 64 to 66°F. If it’s too warm, place the jar in the refrigerator until it reaches the desired temperature.
6. Once it has reached temperature, pour the cultured cream into the hand-held churn and get to work! (If you don’t have the churn, a stand mixer with a whisk attachment achieves the same goal.) The cream will first turn into whipped cream, and then will begin to separate into buttermilk and butter.
7. Line a colander with cheesecloth and place the colander inside a bowl. Pour the butter and buttermilk mixture through the cloth. The buttermilk will collect in the bowl below. Gently tighten the cheesecloth to squeeze out more of the buttermilk from the butter solids, then remove the butter from the cloth and place it directly into the colander. Pour cold water over the butter and knead it gently. This is called “washing” the butter and it will extend the butter’s shelf life.
8. Add salt to taste, if you prefer, and knead the salt into the butter. Salt aids in preservation, so if you keep butter out on the counter, it’s a good idea to add some salt.