Step 1

Preheat the oven to 350 degrees.

Step 2

In an 8 or 9-inch cast iron skillet, melt the butter over medium-low heat. Whisk in the white sugar and brown sugar until smooth.

Step 3

Remove from heat and allow the skillet to cool for 5 minutes (just until it's not hot; warm is okay).

Step 4

Add in the vanilla and egg. Mix until combined. Add in the flour, baking soda, salt, and chocolate chips. Mix until combined.

Step 5

Smooth around the skillet making the center higher than the edges (edges tend to rise more).

Step 6

Bake for 20 minutes. Remove and crumble the graham cracker sheets on top and press the miniature marshmallows into the cookie. Bake for another 5-10 minutes or until cooked through and golden around the edges (it should still be soft and slightly under-baked in the center).

Step 7

Remove and enjoy immediately!