Mix milk, starter, and softened fat in non-reactive bowl (no metal) with half of the flour. Stir well. Add remaining flour and salt and mix well to form a stiff dough. Cover and let sit for 20 to 24 hours, then refrigerate for at least 6 hours…or until you get time to bake!
Preheat oven to 350 degrees F. Pinch off a small amount of dough and put remaining dough back into fridge. Place pinched off dough on a lightly floured piece of parchment paper. Roll out very thin, adding flour as needed to keep dough from sticking to rolling pin. Sprinkle with more salt and lightly roll over dough with rolling pin to help salt stick to dough. Score with sharp knife, pressing lightly to avoid cutting paper or counter. Transfer to oven using a baking peel. Bake for 10 minutes, checking often to make sure crackers are not getting over done. Remove crackers from oven when golden and cool in a big baking dish (I think a 9×13 would be big enough, but Lucinda will have to clarify for us!). Continue baking until all dough is used. Set oven to 200 degrees F. and crisp crackers in the baking dish pan for 1 hour. Store in airtight container. Makes a lot of crackers!!
Recipe by Kelly the Kitchen Kop at https://kellythekitchenkop.com/easy-sourdough-recipes-english-muffins-crackers-pizza-crust-pancakes-and-waffles/