Preheat the oven to 350°F. Coat a 9x13 pan with cooking spray or line with parchment paper.
Cream together the butter and brown sugar until light and fluffy. Add the eggs and vanilla.
In a separate bowl, sift or whisk together the flour, baking powder, and salt.
Add the dry mixture into the butter mixture and mix until fully combined.
Fold the chocolate chips and mini marshmallows into the cookie dough.
Drop the dough onto the baking sheet and spread it to cover the bottom with a spatula. Press the Teddy Grahams into the cookie dough.
Bake cookie bars in the oven for 20 minutes or until lightly browned.
Remove from the oven and let them cool completely before cutting them into squares.
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