Combine the sourdough starter, flour, and water until a firm dough forms. Place it into a lightly oiled jar, cover loosely, and let it rise until domed and active. In cooler weather you can do this overnight the night before.

Add all the ingredients except the butter to a stand mixer fitted with a dough hook. Mix on low speed for about 5 minutes to bring the dough together and begin gluten development.

Add the butter gradually, a few cubes at a time. Increase to medium speed and continue mixing for 10 to 12 minutes, until the dough is smooth, strong, and glossy.

Let the dough rest for 5 minutes, then stretch a small piece. It should stretch thin without tearing.

Place the dough in a lightly greased bowl and let it rise in a warm spot at around 24 to 26°C or 75 to 79°F until it has increased in volume by about 30 to 40 percent. This usually takes 2 to 4 hours, depending on temperature.

Cover and refrigerate overnight. The dough can be cold proofed in the refrigerator for 12 to 36 hours.

The next day, shape the dough according to your recipe. Once shaped, let it proof in a warm spot until puffy and relaxed. Timing will vary depending on what you are making.