Trace an 8" x 12" rectangle on a large piece of parchment paper. Flip the paper over so that you can see the outline but no pencil line will transfer to your dough.
Cut the butter into pieces, each measuring one tablespoon.
Add the ingredients for the pumpkin spice dough to the bowl of a food processor. Process until the dough comes together in a ball.
Transfer the pumpkin spice dough to the parchment paper and break it into 4 pieces. Set this aside.
Add the ingredients for the dark chocolate dough to the food processor. Process until the dough comes together in a ball.
Transfer the dark chocolate dough to the parchment paper and break it into 4 pieces.
Flatten each piece of dough into a small, flat pancake. Stack the pancakes, alternating each dough.
Turn the stacks on their side and then press down on them to make a rough rectangle. Cover this with plastic wrap and then roll it out to closely match the pencil guide on the parchment. Trim the edges and then place the trimmings over the dough to increase the marbling effect. Roll again to the final 8" x 12" rectangle.
If you'd like to add sprinkles to the dough, gently press them into the top of the dough before chilling.
Leave the dough covered and transfer it right on the parchment paper to a sheet pan. Refrigerate the dough for 1 hour.
Preheat the oven to 350°F. Line two sheet pans with parchment paper.
Take the dough from the refrigerator. Cut the dough into 1-inch squares suing a knife or pizza cutter. Use a ruler for the best precision or eyeball it for less uniform cookie bites.
Transfer the squares to the two sheet pans, leaving a bit of space between each piece. Bake for 6 minutes and then rotate the pans from top to bottom racks. Bake for another 5-6 minutes until the cookies have puffed up slightly and the tops are dull and not shiny.
Remove the pans from the oven and allow the cookies to cool completely on the pans. Transfer to an airtight storage container.
Nutrition facts are sometimes provided below and are calculated using an online calculator. With specific brands of ingredients and additions, omissions, or substitutions the nutrition facts may change. We encourage you to use your own nutrition facts calculator to obtain the most accurate nutrition facts for your meal.