Preheat the Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy removal of crackers.
Prepare the Dry Ingredients: In a medium mixing bowl or in the bowl of a stand mixer, whisk together on medium speed the milled wheat flour, baking soda, cinnamon, salt, and brown sugar.
Mix the Wet Ingredients: In a separate bowl, whisk together the softened butter, ½ cup of sourdough starter, water, honey or maple syrup, and vanilla extract.
Combine Wet and Dry Ingredients: Add the wet ingredients to the dry ingredients and stir until combined. The dough should hold together easily and feel similar to soft play-dough. If the dough feels crumbly or dry, add milk one tablespoon at a time until it comes together.
Chill Dough: Once dough is completely mixed, divide the dough in two discs and wrap both in plastic and chill for at least two hour. See Tips.
Roll Out the Dough: Lightly sprinkle a small amount of flour on a piece of parchment paper. Place dough in the center of the parchment paper and sprinkle a small amount of flour on top. Place a second sheet of parchment paper over the dough. Use a rolling pin to roll from the center outward to the desired thickness. About ⅛ inch is ideal for crunchy graham crackers.
Cut the Crackers: Use a cookie cutter, sharp knife, or pizza cutter to cut the rolled-out dough into 2×3 inch rectangles. Transfer the entire sheet of parchment paper (without separating the rectangles) onto a cookie sheet. If you like the store-bought version of graham cracker shapes, you can use a fork to prick the dough in the center of each cracker to give them the signature look.
Bake: Bake in the preheated oven for 15-20 minutes, or until they are lightly golden and crisp.
Cool and Serve: Once baked, they may appear soft at first, but they will begin to crisp up as they cool. Let them cool completely, then break them into individual crackers. Enjoy them as a snack or use them in recipes that call for graham crackers!
