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1
Position a rack in the middle of the oven and preheat to 350 degrees F. Line a 9-inch-square baking pan with aluminum foil, leaving a 2-inch overhang on all sides.
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2
Lightly spray the foil with cooking spray.
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3
Pulse 1 cup pretzel pieces in a food processor until finely ground (you should have about 1/2 cup crumbs).
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4
Transfer to a bowl.
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5
Whisk in the flour, baking powder and salt.
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6
Melt the butter in a saucepan over medium heat.
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7
Remove from the heat and stir in the brown sugar.
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8
Let cool slightly, then stir in the eggs and vanilla.
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9
Stir the pretzel crumb mixture into the butter mixture in two additions.
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10
Spread the batter in the prepared pan.
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11
Scatter the remaining 1/2 cup pretzel pieces on top.
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12
Bake until golden and a toothpick inserted into the center comes out clean with a few crumbs, 25 to 30 minutes.
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13
Let cool completely in the pan on a rack, then lift the foil to remove the bars from the pan and transfer to a baking sheet.
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14
Preheat the broiler.
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15
Press the marshmallow halves, cut-side down, in even rows on top of the bars.
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16
Broil, rotating the baking sheet as needed, until the marshmallows are golden brown, 1 to 2 minutes; let cool.
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17
Put the peanut butter chips and 1/2 teaspoon vegetable oil in a microwave-safe bowl and microwave in 30-second intervals, stirring, until melted and smooth.
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18
Repeat with the chocolate chips and the remaining 1/2 teaspoon vegetable oil in another bowl.
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19
Drizzle the melted peanut butter and chocolate mixtures over the bars.
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20
Let harden at room temperature or chill to set before cutting.
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21
Photograph by Levi Brown
