1-First Step: Prep Your Mise en Place Preheat oven to 375°F. Line two baking sheets with parchment paper to prevent sticking. This setup ensures even baking and easy cleanup. Measure all ingredients ahead. Crush graham crackers in a food processor or zip bag with a rolling pin for uniform crumbs. Softening butter at room temp makes creaming smooth. Pro tip: If butter is cold, microwave 10 seconds.

2-Second Step: Cream the Wet Ingredients In a large bowl, beat 1 cup softened butter, 3/4 cup granulated sugar, and 3/4 cup brown sugar with an electric mixer on medium speed for 2-3 minutes. Mixture should turn light and fluffy. This traps air for tender cookies. Add 1 egg and 1 tsp vanilla extract; beat until combined, about 1 minute. Scrape bowl sides to incorporate fully. Common mistake: overbeating here leads to tough dough.

3-Third Step: Mix Dry Ingredients In a separate bowl, whisk 1 1/2 cups flour, 1 cup graham cracker crumbs, 1 tsp baking soda, and 1/2 tsp salt. Dry mix ensures even distribution. Slowly add to wet ingredients on low speed. Mix just until dough forms, 1-2 minutes. Dough will be soft and sticky. Fold in 1 cup chocolate chips by hand with a spatula for even chunks.

4-Fourth Step: Chill the Dough Cover dough and chill 30 minutes in fridge. Chilling prevents spreading, yielding thicker cookies. For busy schedules, chill up to overnight. This step boosts flavor as sugars meld.

5-Fifth Step: Scoop and Bake Scoop 2-tablespoon mounds onto sheets, 2 inches apart. Bake 10 minutes until edges golden. Remove from oven. Quickly top each with half marshmallow and extra chocolate chips. Broil 1-2 minutes on high, watching closely to toast marshmallows golden. Marshmallows puff and turn gooey.

6-Final Step: Cool and Serve Transfer to wire racks to cool 5 minutes. Cookies firm as marshmallows set slightly. Serve warm for best melt. Pair with milk or coffee. Store leftovers properly (see storage section). Troubleshooting: Flat cookies? Chill longer. Dry? Add 1 tbsp milk to dough.