Mud Hen Bars

Ingredients

• Cooking spray
• 6 tablespoons (3/4 stick) unsalted butter, at room temperature
• 1 large egg, at room temperature
• 2/3 cup granulated sugar
• 1/4 teaspoon kosher salt
• 1 teaspoon vanilla extract
• 1 cup all-purpose flour
• 3/4 teaspoon baking powder
• 2/3 cup semi-sweet or bittersweet chocolate chips
• 1/2 cup miniature marshmallows
• 2 large egg whites, at room temperature
• 2/3 cup packed dark or light brown sugar
• 1/4 teaspoon vanilla extract
• 1 pinch kosher salt

Method

1. Make the cookie base:
2. Heat the oven to 350°F. Coat an 8x8-inch square baking pan with cooking spray. Line the pan with 2 sheets of parchment paper, positioning them perpendicular to each other and making sure they are long enough to hang over the edges by at least 2 inches to form a sling.
3. Beat 6 tablespoons room-temperature unsalted butter, 2/3 cup granulated sugar, and 1/4 teaspoon kosher salt together in a stand mixer with the paddle attachment on medium speed until light and fluffy, about 2 minutes.
4. Reduce the speed to low. Add 1 room-temperature large egg and 1 teaspoon vanilla extract, and beat until combined, scraping down the sides of the bowl with a flexible spatula as needed.
5. Turn the mixer off. Add 1 cup all-purpose flour and sprinkle the surface with 3/4 teaspoon baking powder. Beat on medium speed until just combined and the texture of thick cake batter.
6. Transfer the dough to the baking pan and spread into a smooth, even layer. Sprinkle 2/3 cup semi-sweet chocolate chips and 1/2 cup miniature marshmallows evenly over the top.
7. Make the meringue:
8. Wash and dry the stand mixer bowl. Beat 2 room-temperature large egg whites, 2/3 cup packed brown sugar, 1/4 teaspoon vanilla extract, and 1 pinch kosher salt together in the stand mixer with the whisk attachment on high speed until medium, shiny peaks form, 4 to 5 minutes. Transfer onto the cookie base and spread into an even layer.
9. Bake until golden-brown and the top begins to crack, 28 to 30 minutes.
10. Place on a wire rack and let cool until just warm or at room temperature, at least 1 hour. Grasping the excess parchment, lift the slab out of the pan and place on a cutting board. Cut into 9 pieces; for the cleanest-looking slices, wash the knife and wipe dry between cuts.
11. Recipe Notes
12. Storage: Store in an airtight container at room temperature for up to 1 day. The meringue top will soften and get sticky over time.