Some tips I learned:
1. If your jam/preserves are thick, try heating them in the microwave for 10 seconds- this will make it easier to spread.
2. Try your best to evenly distribute the the dough over the preserves- mine didn't spread that much, leaving a lot of preserves "bare" spots.
1/2 pound (2 sticks) unsalted butter, at room temperature
1-1/2 cups sugar
1 tsp pure vanilla extract
2 extra-large eggs, at room temperature (Used 3 large eggs)
2 cups (18 ounces) creamy peanut butter (recommended: Skippy)
3 cups all-purpose flour
1 tsp baking powder
1-1/2 tsp kosher salt
1-1/2 cups (18 ounces) raspberry jam or other jam (Used strawberry preserves)
2/3 cups salted peanuts, coarsely chopped (Omitted)
1. Preheat the oven to 350 degrees F.
2. Grease a 13x9x2 cake pan. Line it with parchment paper, then grease and flour the pan.
3. In the bowl of an electric mixer fitted with the paddle attachment, cream the butter and sugar on medium speed until light yellow, about 2 minutes.
4. With the mixer on low speed, add the vanilla, eggs, and peanut butter and mix until all ingredients are combined.
5. In a small bowl, sift together the flour, baking powder, and salt.
6. With the mixer on low speed, slowly add the flour mixture to the peanut butter mixture. Mix just until combined.
7. Spread 2/3 of the dough into the prepared cake pan and spread over the bottom with a knife or offset spatula.
8. Spread the jam evenly over the dough.
9. Drop small globs of the remaining dough evenly over the jam.
10. Sprinkle with chopped peanuts and bake for 45 minutes, until golden brown.
11. Cool and cut into squares.
Yield: 24 large bars (can be but smaller)
Source: Ina Garten