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Preheat oven to 375 degrees and line a baking sheet with parchment paper. Set aside.
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In a large bowl, beat butter until light and fluffy, about 1 minute. Add in both sugars, and cream until well combined. Add in eggs, one at a time, beating well after each addition. Set aside.
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In a separate bowl, sift together flour, cocoa powder, baking soda, salt, and espresso powder.
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Alternately add the dry ingredients and the buttermilk and water to the butter mixture, beginning and ending with the dry ingredients. Stir in vanilla extract.
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(The batter will be a consistency in between cookie dough and cake batter).
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Drop dough by large Tablespoons onto the prepared cookie sheet, spacing each about 2" apart.
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Bake for 6-7 minutes, or until the cookies are set (puffy but soft to the touch). Allow to cool completely before frosting.
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In a bowl, beat butter and marshmallow creme until well combined. Add in heavy cream, vanilla extract, and 1 1/2 cups powdered sugar. If the filling is too thin, add in the remaining 1/2 cup of powdered sugar. Add in a pinch of salt to cut the sweetness, if desired.
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With a piping bag, add frosting to the flat side of half of the cookies. Top with remaining half of cookies and slightly press down.
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Roll the edges of cookies in crushed graham crackers.
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Enjoy!