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1
Preheat the oven to 350 degrees F. Cut a piece of foil 9 by 20-inches.
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2
Butter the corners and sides of a 9-by-13-inch baking pan.
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3
Line the pan with the foil so that the excess hangs over at each of the short sides of the pan.
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4
Whisk the flour in a medium bowl with the baking powder, baking soda and salt.
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5
Whisk in 1/2 cup peanuts.
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6
Put the melted butter in a large bowl and use a rubber spatula to stir in the sugars.
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7
Stir vigorously, mashing the brown sugar lumps with the spatula, so that the mixture is well combined and creamy.
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8
Using the rubber spatula, stir in the peanut butter, again making sure the mixture is well combined.
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9
Stir in the eggs and vanilla.
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10
Fold in the flour mixture until just combined.
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11
Scrape the batter into the prepared pan.
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12
Press the back of a spoon or a curved rubber spatula into the batter to make little wells all over the batter, making sure not to push down to the bottom of the pan.
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13
Spoon the jam into the wells, making sure the jam is distributed evenly across the pan.
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14
Use a knife to pull the jam through the peanut butter mixture-it won't exactly ribbon, you will end up with some chunks of jam throughout.
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15
Sprinkle the remaining 1/2 cup chopped peanuts over the top.
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16
Bake until a toothpick inserted in the center of a non-jammy spot comes out clean, about 35 minutes.
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17
Cool completely on a rack, about 1 hour.
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18
When the bar has cooled completely, place a lightweight cutting board or a baking rack over the top of the pan.
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19
Flip and set on the counter.
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20
Gently pull the pan from the foil and the foil from the pan to remove.
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21
Gently peel the foil off the bar.
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22
Place another lightweight cutting board on top, and flip the bar right-side-up.
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23
For easier slicing, wrap with plastic wrap, and let sit at room temperature overnight.
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24
Cut into forty eight 1 1/2-inch squares.
