6 tablespoons room-temperature bacon fat, or similar fat
1½ cups whole wheat flour
Place the sourdough starter in a medium bowl. Stir in salt, rosemary, peppercorns, and bacon fat until thoroughly blended.
Add sifted whole wheat flour. Mix well, using clean hands, if necessary.
Knead the dough briefly right in the bowl. Cover and proof 8 hours or overnight.
Preheat oven to 350°F.
Divide dough into three sections. Roll out each portion as thin as possible on parchment paper.
Score the dough in 2-inch squares, using a rolling pizza cutter or a sharp knife. Prick each square with the tines of a fork to keep the dough from puffing up as it bakes. Sprinkle the dough with additional sea salt and pepper, if desired, pressing it lightly into the dough with the palm of your hand.
Slide the parchment paper onto a baking sheet. Bake in a for about 15 minutes, checking frequently after 10 minutes to make sure crackers are not getting too brown. You may need to remove the outer rows of crackers before the center rows are fully baked, as the entire tray of dough does not always bake evenly. Crackers should be a nice golden brown, not dark brown, and thoroughly dry to the touch.
Cool on a rack, separating any crackers that did not already break apart at the score lines. Store in an air-tight container at room temperature for a week or freeze for longer storage.
Note: This dough can be frozen after it has proofed overnight. Defrost 1-2 hours before rolling out and baking as directed above.