Brown the butter in a small saucepan over medium heat until bubbly, dark, and golden in color. Be sure to stir it continuously, being careful to not burn it.

Remove from heat and allow the butter to cool completely to room temperature.

In a mixing bowl, combine the dry ingredients (flour, baking soda, baking powder, & salt).

Once the butter has cooled but is still liquid, to a stand mixer, add the brown butter, sugar, vanilla extract, and sourdough starter. Mix with the paddle attachment until smooth and fully incorporated.

Add the dry ingredients into your stand mixer with the wet ingredients. Stir until just combined. Be sure to not over-mix the dough.

Add your chocolate chips, graham crackers, and marshmallows. Give it two stirs on low speed just to get them to be fully incorporated into the dough. You can also mix these in by hand.

Place the dough in the fridge for at least 2 hours to chill, covered.

Line a cookie sheet with parchment paper or a silicone baking mat. Scoop about 2 tablespoons of your chilled cookie dough and shape into balls.

Preheat the oven to 375° and place the cookie dough balls about two inches apart on the lined cookie sheet.

Bake for 12 minutes. Remove from the oven. Tap the pan down onto your stove or countertop to get the cookies to flatten out a bit and get that perfect cookie shape. Use a knife to push any marshmallows that may be oozing out the sides.

Allow for cookies to sit on the baking sheet for at least another 5 minutes. Enjoy!