How to Make It
Preheat the oven to 350°. Line 2 large baking sheets with parchment paper. In a medium bowl, whisk the flour, baking soda and salt. In another medium bowl, using a hand mixer, beat the butter with both sugars at medium speed until light and fluffy, about 3 minutes. Beat in the egg and vanilla, then beat in the dry ingredients in 3 batches, mixing well between additions. Fold in the peanut butter until fully incorporated.
Scoop 24 one-inch balls of dough onto the baking sheets at least 2 inches apart. Press the balls down slightly; they should be about 1 1/2 inches in diameter. Sprinkle the tops with the chopped peanuts. Bake the cookies for 10 to 12 minutes, until the edges are light golden brown and the tops are slightly cracked; rotate the baking sheets halfway through. Let the cookies cool for 10 minutes on the baking sheet, then transfer to a rack to let cool completely.
In a bowl, using a hand mixer, whip the peanut butter with the butter, confectioners’ sugar, vanilla and salt at medium speed until fluffy, about 5 minutes. Refrigerate for about 45 minutes, until chilled.
Spoon 1 1/2 tablespoons of the filling on the underside of 12 cookies. Spread 1 teaspoon of jam on the underside of the remaining cookies. Sandwich the halves together and serve.