1-Roughly chop the graham crackers and the chocolate bar, and tear the mini marshmallows in half to prevent puffing too much during baking.

2-Combine the flour, salt, baking powder, baking soda, and cornstarch in a bowl and whisk together.

3-Using a stand or hand mixer, beat the butter and sugars until creamy, about 2 minutes. Add the egg and vanilla extract, and mix until combined. Scrape the bowl and mix again.

4-Gradually add the dry flour mixture to the butter mixture on low speed until just combined.

5-Reserve a handful of the torn marshmallows; add the remaining marshmallows, chocolate chips, and chopped graham crackers to the dough, mixing gently to distribute.

6-Refrigerate the dough for at least one hour.

7-Preheat the oven to 350°F.

8-Portion the dough into two-tablespoon-sized balls, roll them, and place them on a parchment-lined baking sheet spaced about 2 inches apart.

9-Bake for 8 minutes, then top the cookies with the reserved marshmallows and chocolate pieces.

10-Return to the oven for an additional 2 to 3 minutes to finish baking.

11-If the marshmallows spread too much during baking, use a round cookie cutter or knife to push the edges back together immediately after removing from the oven.

12-Allow the cookies to cool completely on the baking sheet to firm up.