Make the crust: Whisk the salt and all-purpose flour together in a large bowl.
200 grams all-purpose flour, 7 grams salt
Toss the butter in the flour mixture, squeezing and rubbing the butter into the flour. Dissolve the discard in the water.
226 grams unsalted butter
Create a well in the center of the flour and pour the dissolved discard into the center. Stir the mixture together until most of the flour looks hydrated.
113 grams sourdough discard, 75 grams water
Lightly knead the mixture until it comes together into a shaggy dough, a few bits of dry flour is OK, don't be tempted to add more water to the mixture.
Turn the dough out on to a large piece of plastic wrap. Flatten the dough out into a rectangle about 8 by 10 inches (this doesn't have to be exact). Make sure the dough is completely wrapped so that it doesn't dry out. Let the dough rest for 15 minutes. This will make it much easier to laminate.
Laminate the dough: Unwrap the dough and turn it out onto a heavily floured surface.
Complete Book Fold: Using a rolling pin, flatten the dough out into a large rectangle (about 18 by 8 inches, it doesn’t have to be exact). Fold the short sides towards so they meet in the center. Fold the dough in half and let it chill for 30 minutes.
Complete Letter Folds: Roll the dough out into a long rectangle (about 24 by 8 inches long). Fold the sides towards the center, overlapping like you’re folding a letter. Complete 2 to 3 letter folds in 30 minute intervals. Wrap the dough and chill it in between folds. The dough should look cohesive and the butter will look more evenly distributed after the last fold. Store: Wrap the dough back up in plastic and refrigerate for at least 2 hours before using.