Preheat oven to 375 degrees. In a medium bowl, whisk to combine the flour, graham cracker crumbs, salt and baking soda.
In a large bowl, whisk to combine the melted butter, granulated sugar, light brown sugar, eggs and 1/4 cup peanut butter. Add the flour mixture and stir to combine then fold in 1/2 cup Reese's pieces and 1/2 cup marshmallows.
Transfer half of the dough into a 12-inch cast iron skillet and spread to make even. Smooth over 2 cups peanut butter and top with 2 cups mini marshmallows. Top with remaining dough and sprinkle over remaining 1/4 cup Reese's pieces, 1/2 cup mini marshmallows, graham cracker pieces and mini chocolate candy bars.
Bake cookie for 35-38 minutes. Drizzle remaining 1/4 cup warmed peanut butter over the top and sprinkle over remaining Reese's pieces. Mound 1/2 cup marshmallows in the center of the cookie. Use a kitchen torch or broiler to toast, about 1 minute. Let the cookie sit for 10-15 minutes, then slice to serve.