I looked back at my recipe, and it made me laugh because the first step is to make crème fraîche using buttermilk, but I think you could use a bit of yogurt for that step. The recipe makes cultured buttermilk and butter, so you just need something to culture the cream first (this is what makes it so delicious in my opinion).
One pint (2 cups) of cream will yield about 6 ounces of butter and 3/4 cup buttermilk, but this will depend on the fat content of your cream.
1. Culture the cream (make crème fraîche) by adding 2 tablespoons of buttermilk (or yogurt?) to 2 cups of heavy cream. Place in a sealed jar and keep at room temperature for 12-36 hours until thick. Mine took 20 hours to set. Ultra-pasteurized cream will take longer than pasteurized. Refrigerate cream after it sets.
2. Pour the cream into a food processor and blend until butter separates from the butter milk. This takes about 5 minutes.
3. Pour contents in a strainer over a bowl to remove buttermilk. Reserve buttermilk.
4. Return butter to processor, add ice cold water, and pulse to clean the butter. Drain liquid and repeat 2-3 times until water is no longer cloudy.
5. Place butter in a bowl and mash with a potato masher or fork to remove remaining water. Tilt bowl and pour off water as it accumulates.
6. Knead in a few pinches of salt if desired, mold butter, and refrigerate.
I should add that I haven’t tried to bake with this, but it does taste just like buttermilk from the store—actually even better as it is fresher and will have a few little specks of butter in it.