Melt the butter in a microwave-safe bowl in the microwave, or in a small saucepan over medium-low heat on the stovetop. While it’s still hot, pour the butter into a large bowl. Add the brown sugar, and stir well. Stir in the egg and vanilla, and then the peanut butter. Add the flour, baking soda, and salt, and stir to combine.

Refrigerate the dough for 20 minutes. Meanwhile, preheat the oven to 350F and line 2 large baking trays with parchment paper.

Once the dough is chilled, roll it into 2-tablespoon-sized balls and arrange them evenly on the prepared baking trays.

Bake for 10 minutes (rotating once halfway through), then remove the cookies from the oven and use a 1/2-tablespoon measuring spoon to make an indentation in the center of each cookie. Fill each indentation with 1 teaspoon jam. Return the cookies to the oven and bake until they’re set and golden on the bottom, about 8 minutes, rotating the trays once halfway through. Cool to room temperature, and then decorate.

To make the peanut butter ganache, warm the peanut butter and white chocolate chips together until the chocolate is melted and the mixture is smooth. Drizzle the ganache on the cooled cookies, and immediately sprinkle on the finely chopped peanuts.

Let the ganache set before serving.