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1
Preheat the oven to 350 degrees F. Line an 8-inch square baking dish with aluminum foil, leaving a 2-inch overhang on the ends of the pan for lifting out the finished bars.
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2
Stir together the ground grahams, flour, sugar and salt in a small bowl.
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3
Cream the butter, egg and vanilla in a medium bowl with an electric mixer on low speed until creamy and combined; you are not trying to beat a great amount of air into the mixture.
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4
Add the graham mixture and continue to beat on low speed until just combined and large crumbles form.
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5
Place about two-thirds of the mixture in the prepared pan and firmly press down.
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6
Reserve a few pieces of the chocolate for garnish (about 1/2-ounce), and then scatter the rest of the chocolate pieces over the base.
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7
Drop spoonfuls of the marshmallow creme over the chocolate, stretching the creme so it covers more of the base.
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8
Drop the remaining cookie batter in small clusters over the chocolate and creme so the creme is mostly covered.
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9
Bake until the dough is golden brown and the cookie in the center of the pan feels firm, about 40 minutes.
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10
The marshmallow creme will puff through the crumble and brown, and it will deflate as it cools.
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11
Cool in the pan at least 15 minutes.
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12
Using the foil overhang, lift the crumble bars out of the pan.
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13
Melt the reserved pieces of chocolate in the microwave in 30-second intervals until smooth, and then drizzle over the cookies.
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14
Cut into sixteen 2-by-2-inch squares.
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15
Serve warm or at room temperature.
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16
Cook's Note: Working with marshmallow creme can be a sticky experience.
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17
A light coating of nonstick cooking spray or vegetable oil in your measuring cup and on your spatula or spoon can make it a bit easier to work with.
