Preheat oven to 400 degrees F. Line two cookie sheets with parchment paper.

In a medium mixing bowl, combine the flours, baking soda, and salt by whisking them together. (Include optional herbs and spices if desired.) Use a pastry cutter or fork to incorporate the cold butter into the dry ingredients.

In a small bowl, mix the starter, water, and egg with a whisk. Add this mixture to the flour and butter blend. Stir until a stiff dough forms. Knead for a few minutes to combine the dough. If the dough is sticky, sprinkle your hands with tapioca flour. If it's too dry, moisten your hands or add a tablespoon of water.

Divide the dough in half and place them on parchment paper. Roll the dough out to just under 1/4".

Tip: Press the dough down to flatten slightly, then very lightly dust with tapioca flour, place a piece of parchment paper on top to assist with rolling out. Peel the top parchment paper off when the dough is the right thickness. This makes it much easier to get a thin dough.

Using a pastry cutter or a pizza cutter, slice the dough into 1-1/2" squares. Pierce each square several times with a fork. Transfer the parchment paper onto a large cookie sheet. Repeat the process for the second ball of dough.

Place the cookie sheet onto the middle racks of preheated oven. Bake 10-12 minutes or until the edges begin to turn a golden brown.

Remove from oven and allow to cool. Store in airtight container for up to one week.