In a large bowl, add the all-purpose flour, whole wheat flour, salt, sugar, room-temperature butter, yeast, sourdough discard, and warm water(105-110°F).

Combine the ingredients until the dough is smooth, elastic, and slightly sticky this should take 12-15 minutes.

For best results, perform the windowpane test to ensure proper gluten development. If the dough feels too sticky, add a little more flour, a tablespoon at a time, as needed. Cover the dough with a damp cloth or plastic wrap and let it rest for about 30 minutes.

To perform a stretch and fold, gently lift one side of the dough and fold it over to the other side. Turn the bowl a quarter turn and repeat the process until you’ve folded each side (4 times in total). Rest the dough for 30 minutes, then repeat the stretch and fold process. Perform a total of 2–3 sets of stretch and folds, with 30 minutes of rest in between each set.

Cover the bowl with a kitchen towel or plastic wrap, and let it rise in a warm place for about 1–1.5 hours, or until it doubles in size.

After the dough has doubled, punch it down so that air bubbles are released, then divide it into two equal portions. Shape each portion into a log shape by gently pressing it into a rectangle and rolling it up from the short end.

Preheat your oven to 350°F (175°C). After the loaves have risen, bake them for 30–35 minutes, or until they turn golden brown and their internal temperature reaches 190°F (88°C).

Remove the loaves from the oven and let them cool in the pans for about 10 minutes. Then, transfer them to a cooling rack to cool completely. For storage, keep them in plastic bread bags or an airtight container for 5–7 days.