Makes 12 ounces of Butter

Prepare the Cream:

• In a bowl, add the heavy cream. The cream should ideally be high-fat (36-40%).
  
• To the cream, add 4 tablespoons of cultured buttermilk. Make sure the buttermilk is labeled as 'cultured'.
• Add 1 cup of plain yogurt to the bowl. It should also be cultured.
  
• Mix all the ingredients well and cover the bowl.
• Leave the mixture at room temperature for 24-48 hours. This allows the cultures to ferment the cream.

Chill the Mixture:

• After the cream mixture has cultured at room temperature, transfer it to the refrigerator and chill it for at least 2 to 3 hours, along with the whisk and bowl you'll be using for the next step. 
• This ensures that everything is cold which is required for making butter.

Whipping the Chilled Cream Mixture:

• Remove the cream mixture from the refrigerator and start to whisk it in your mixer or food processor. Begin at a slow speed due to the thickness of the mixture.
  
• Continue to whip the mixture until it turns into a thick whipped cream. Remember to clean the sides of the bowl with a spatula occasionally to ensure all of the mixture gets whipped.

Forming the Butter:

• Once the whipped cream begins to separate and form lumps (this indicates the butter is forming), switch from a whisk to a paddle attachment or spatula, if possible.
  
• You'll have to be a bit careful in this stage to prevent buttermilk from splattering. Do this on slow speed.
  
• Stop when the butter forms a large block and has released the buttermilk.
  

Rinse the Butter:

• Remove the butter from the bowl and place it in a colander.
  
• Over the colander, press the butter together to remove as much buttermilk as possible. 
  
• The buttermilk will drain away through the colander. This is important as the leftover buttermilk can make your butter go bad quickly.
• Transfer the butter to a bowl of ice water and knead it like dough. This helps to wash out the remaining buttermilk. The water will become milky.
  
• Repeat this washing process two or three times until the water remains clear.

Salt the Butter:

• If you want to add salt to your butter, calculate it based on the grams of the butter. For example, for 350 grams (12 oz) of butter, use about 3.5 grams of salt.
  
• While mixing the salt into the butter, any residual buttermilk will be squeezed out. Remove this as well.
  
• After mixing the salt, give the butter a final rinse in cold water.

Final Steps - Form and Store the Butter:

• Pat your butter dry and shape it however you like. You can even cut it into small pieces or form it into a log.
  
• Your homemade cultured French butter is ready to use! It can be used right away, stored in the fridge, or even frozen for later use.
• Enjoy the delicious homemade butter with a distinct European flavor that you won't find in store-bought versions. You can use it in your cooking, spread it on your favorite bread, or even add it to a freshly baked croissant!