In a medium bowl, combine cooled butter, sourdough starter, and flour. Mix with a spatula until well blended. Cover and set aside in a warm place to ferment for 4 to 8 hours. 

After dough is done fermenting, add cheese, spices, baking soda, and salt to the dough. Mix well with a spatula until fully incorporated. Dough will puff slightly.

Preheat oven to 350º. Position one rack in top third of oven and another rack in bottom third.

Line two baking sheets with parchment paper. Divide dough in half and shape the dough into a log. Use plenty of flour on one of the sheets of parchment and roll out the dough directly on the parchment to roughly the size of the baking sheet, using more flour as needed to prevent sticking. Cut the rolled-out dough into 1” squares with a pizza cutter or pastry crimper. Using a chopstick, poke a hole in the center of each square. Repeat with remaining dough. Sprinkle with a little finishing salt.

Bake for 15 minutes then rotate pans from top to bottom. Bake until crisp, 10 to 15 minutes more. Turn off heat and allow to cool in oven with the door cracked open.

Store crackers in an airtight container for up to two weeks. 

NOTES 

*Sourdough Starter Guide: Make your own in seven days.

Using a scale ensures perfect consistency of the dough.

Finely grating the cheese takes some time but will result in the cheese incorporating into the dough easily.

Use fun cutout shapes like tiny fish for goldfish crackers