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Preheat oven to 350 degrees and grease a 24-cup mini muffin tin well with baking spray. Set aside.
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Beat butter, brown sugar, and granulated sugar together until well combined (using a hand mixer, standing mixer, or by hand).
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Add in the egg, mixing until combined.
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Add in vanilla extract, baking soda, espresso powder and salt, mixing until combined.
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Next, add in graham cracker crumbs, cocoa powder and flour. Mix until well combined.
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Using a 1” cookie scoop (about 1 Tbsp) disperse dough evenly between the muffin cups.
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Bake for 10 minutes, or until the tops are done and the centers have risen (once you take the cookie cups out of the oven, the centers might sink a bit, which is fine).
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Immediately, or within a couple of minutes, press centers down to form a cup shape (I used a tsp to do this). Allow to cool completely before removing from the tin.