In a large bowl, combine the discard, all-purpose flour, butter, and salt. Mix until you get a smooth texture.
Divide the dough into two pieces and shape each one into a rough rectangle. Wrap them in plastic wrap and refrigerate for at least 30 minutes.
Lightly flour a work surface. Roll out the dough to about 1/16" thick. Optionally, add poppy seeds, sesame seeds, roasted garlic, or any other toppings you'd like and roll them gently into the dough.
Transfer the dough to a sheet of parchment paper. Poke the dough all over with a fork. Slice it into 2-inch squares or your preferred shapes. Place onto a sheet pan.
Bake at 350°F for about 25 minutes or until the crackers are golden brown. Halfway through baking, move the crackers around the baking sheet to promote even cooking.
Remove the crackers from the baking sheet to a wire cooling rack. Let them rest and cool to room temperature before serving.