• Day 1: Prepare Cookie Dough for Fermentation

Cookie Dough

• In a large bowl, cream together softened butter, powdered sugar, and brown sugar until light and fluffy.
• Add egg, vanilla extract, and almond extract (if using), mix well.
• Add sourdough starter and mix until combined.
• In a separate bowl, whisk together flour, baking powder, salt, and cream of tartar.
• Gradually add dry ingredients to wet ingredients, mixing until just combined.
• Wrap in plastic and refrigerate for 12-24 hours.

Crumble

• In a food processor, add flour, brown sugar, powdered sugar, and salt.
• Pulse 3-4 times to combine dry ingredients.
• Add graham crackers and pulse until you have large chunks.
• Add cold cubed butter and pulse until combined.
• Add vanilla and sourdough starter, pulse to incorporate.
• Continue pulsing until you reach a brown sugar texture that you can squeeze together and it holds its shape, but also breaks apart easily.
• Refrigerate for 12-24 hours alongside the cookie dough for fermentation.

No food processor?

• Place graham crackers in a zip-top bag and crush with a rolling pin until you have a mix of small chunks and fine crumbs. Whisk together the crushed graham crackers, flour, brown sugar, powdered sugar, and salt in a medium bowl. Add cold cubed butter and cut in with a pastry cutter or your fingertips until the mixture resembles coarse crumbs with pea-sized pieces remaining. Add vanilla and sourdough starter and continue cutting in until the mixture holds together when squeezed but crumbles apart easily. Work quickly so the butter stays cold. If the mixture feels warm or greasy at any point, refrigerate the bowl for 10 minutes before continuing.

Day 2: Assembly and Baking

• In a small bowl, toss mini marshmallows with cornstarch to lightly coat.
• Place cornstarch-coated marshmallows in the freezer for at least 30 minutes before assembly.
• Have chocolate chunks ready for assembly.
• Preheat oven to 350°F (175°C).
• Line a large baking sheet with parchment paper.
• Using a 2.5-3 inch circle cutter as a guide, spread about 2 rounded tablespoons of graham cracker crumble mixture on the parchment in circles. For a marbled effect, leave small gaps between crumble pieces to allow marshmallow and chocolate to peek through.
• Sprinkle chocolate bar chunks evenly over each crumble circle (about 1 teaspoon per cookie).
• Embed frozen, cornstarch-coated marshmallows into the crumble (about 1 teaspoon per cookie or 4-5 mini marshmallows).
• Roll out the fermented cookie dough on a floured surface to a rough rectangle, 10″x 12″, approximately 3/8″ inch thick.
• Using your circle cutter, cut out circles from the dough.
  
• Gently gather scraps, press together into a ball and wrap well. Refrigerate for 15 minutes for gluten to relax before rolling again.
• When ready to assemble the next tray create another rough rectangle and continue cutting until all dough is used.
• Place each cookie circle on top of the chilled s’mores layers.
• Gently press down to adhere, making sure the graham crumble, chocolate chunks, and marshmallows are under the cookie.
• Bake for 18-22 minutes, until you can see golden browning on the graham cracker edges and cookie tops are set.
• Remove from oven and let cool completely on the baking sheet before serving.