For the butter, mix cream and yogurt together until incorporated. Place in a jar and lightly put the lid on, don’t tightly seal. Let sit at room temperature for 24-48 hours until the mixture has thickened to the consistency of thin sour cream. Chill completely.
Whip the cultured cream until the cream breaks and the fat separates. Remove the butter from the buttermilk and rinse the butter in cold water until the liquid coming off the butter turns clear. Now you have cultured butter!
Whip butter with the maple syrup and salt until light and fluffy. Set aside.
For the bread, in a large bowl, whisk flours, salt, and yeast until combined.
Add water and yogurt, and mix until everything is incorporated. (it will be sticky)
Scrape down the sides of the bowl and cover with plastic wrap.
Let rise on the counter for 5 hours.
Heavily flour your hands and a clean surface. Transfer the dough to the heavily floured surface.
Shape dough by folding the side of the dough closest to you up, and then each side of the dough in towards each other. Next, fold the farthest side of the dough in towards yourself. Then, using the side closest to you, flip the dough all the way over so that what was once the bottom of the dough is now the top. (see video)
Using cupped hands, shape the dough into a tight uniform ball. (see video)
Carefully transfer dough to a cornmeal dusted piece of parchment paper. It’s ok if it is a bit misshapen. This is a very forgiving bread! It’s rustic :)
Cover dough with a large bowl, and let rest 30 minutes.
While the loaf rests, preheat your oven to 450ºF with a cast iron dutch oven inside.
Remove the cast iron from the oven. Transfer dough to the hot cast iron. Score loaf as desired. You can use a lame or even just a sharp knife. (see video)
Cover with cast iron lid and place back into the oven. Bake for 30 minutes.
Carefully remove lid from cast iron and return bread to the oven to finish browning and cooking. This next baking step will take about 10-15 minutes depending on how brown you like it.
Remove bread from oven and carefully transfer to a wire rack to cool.
Cool at least 20 minutes before slicing into the loaf! Yum! Serve with the whipped butter.
Notes
* If you don’t want to make the butter itself, you can just substitute 1 stick of unsalted butter, and whip that with the maple and salt!