1cupgraham cracker crumbsapproximately 9 full graham crackers
1/2cup(113g) unsalted buttersoftened to room temperature
3/4cup(150g) firmly packed brown sugar
1 and 1/2teaspoonsvanilla extract
17-ounce jar(198g) marshmallow creme
1cup(175g) milk chocolate chips
Preheat the oven to 350°F (177ºC). Line an 8" square baking pan with aluminum foil, leaving enough overhang on the sides. Spray with non-stick spray. Set aside.
In a medium size bowl, whisk together the flour, graham cracker crumbs, baking powder, salt, and cinnamon. Set aside.
In a large bowl using a handheld mixer or the bowl of a stand mixer fitted with the paddle attachment, cream the butter and brown sugar together on medium speed until mixture is creamy and smooth. Add the egg and vanilla extract. Continue to mix until combined, scraping down the sides of the bowl as necessary.
Turn the mixer down to low speed and slowly add the dry ingredients to the wet ingredients. Mix until combined.
Press approximately 2/3 of the graham cookie dough evenly into the prepared pan. Spread the marshmallow creme on top. I find the best way to do this is to scoop out the entire amount of creme into the middle of the dough, spray a spatula generously with non-stick spray, and spread it as best as you can. Sprinkle the marshmallow layer evenly with the chocolate chips.
Mold the remaining cookie dough into 5 or 6 flat pieces and layer on top of the chocolate chips. Spread around with your hands the best you can. If some chocolate chips and marshmallow spots are exposed, that's completely ok.
Bake the bars for 26-28 minutes, or until the top is lightly golden brown and the spots of marshmallow creme that stuck out are just beginning to brown. Allow to cool completely on a wire rack before cutting into squares. Bars stay fresh covered tightly at room temperature up to 1 week. Bars may be frozen up to 3 months. Thaw overnight in refrigerator or warm up individually in the microwave for 15-20 seconds.