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1
Preheat the oven to 350 degrees F. Line a 9-inch square pan with a piece of aluminum foil (about 17 inches long), leaving a 2-inch overhang on each side.
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2
Lightly coat the bottom and sides of the lined pan with cooking spray.
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3
Melt half the butter (4 tablespoons) in a medium bowl in the microwave, about 45 seconds.
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4
Set aside 1 cup of the cake mix, and add the remaining mix to the melted butter.
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5
Add the egg and 1 tablespoon water, and mix with a spatula until well blended.
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6
Let stand a few minutes until the mixture is no longer tacky to the touch.
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7
Pat the dough in an even layer in the pan.
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8
Bake until the edges are lightly set to the touch and the crust is lightly browned all over, about 20 minutes.
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9
Let cool for 5 minutes.
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10
Meanwhile, melt the remaining butter in a medium bowl in the microwave, about 45 seconds.
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11
Add the reserved cake mix, oats and cinnamon, and mix with a fork until crumbly.
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12
Spread the apple butter over the cooled crust, spreading it to the edges.
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13
Scatter the crumb mixture over the apple butter.
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14
Return the pan to the oven and continue to bake until the crumbs are golden brown and firm, about 30 minutes more.
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15
Cool completely in the pan.
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16
Using the foil overhang, lift the bars out of the pan and peel the foil away from the edges.
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17
Dust with confectioners' sugar, and cut into 16 bars.
