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1
Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
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2
Sift together the flour, baking powder, baking soda, and salt into a medium bowl and set aside.
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3
Place the butter, granulated sugar, and light brown sugar in the bowl of an electric mixer and cream the ingredients on high speed.
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4
Scrape down the sides of the bowl with a rubber spatula.
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5
Add the vanilla and egg and mix on medium speed.
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6
Add the flour mixture and mix on low speed just until batter is stiffdon't overdo it!
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7
Turn off the mixer and, using a large spoon or plastic spatula, fold in the chocolate chips and the walnuts, if desired.
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8
Using a tablespoon, scoop about 2 spoonfuls of the dough into a ball and place on the baking sheet.
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9
Repeat with remaining dough, keeping the scoops about 2 inches apart.
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10
Using your fingers or the back of the spoon, press down on each ball of dough to slightly flatten.
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11
(You should get about 9 cookies on each sheet.)
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12
Bake until golden brown, about 20 minutes.
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13
(Depending on the size of your oven, you may need to do this in batches.)
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14
Using oven mitts or pot holders, remove the cookies from the oven and transfer with a plastic turner to wire racks to cool.
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15
Repeat with the remaining sheets, if necessary.
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16
Filling:
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17
In the bowl of an electric mixer, combine peanut butter, powdered sugar, vanilla, and chocolate sauce and beat well.
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18
With a thin metal pastry spatula or a butter knife, spread a layer of the peanut butter filling on the bottom of a cookie.
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19
Press another cookie over the filling to make a sandwich.
