Peanut Butter Jelly Bars

Ingredients

• For the jelly:
• 1 pound Concord grapes
• 1 cup sugar, divided
• 1 1/2 teaspoon lemon juice from 1 lemon
• For the bars:
• 1/2 cup unsalted butter, melted and cooled
• 3/4 cup white sugar
• 3/4 cup plus 1 tablespoon dark brown sugar
• 2 eggs
• 4 teaspoons vanilla
• 1 cup smooth peanut butter
• 1 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1 teaspoon salt
• 1/2 cup roasted unsalted peanuts, roughly chopped
• 1 cup grape jelly

Directions

1. For the jelly: Slip the grapes out of their skins with a gentle squeeze, dropping the pulp into a large saucepan or a wide-bottomed pot. Put the skins in a blender with 1/2 of the sugar and pulse them into a coarse mixture, then scrape that into the pot with the remaining sugar and the lemon juice. Set the pot over medium heat and cook at a gentle boil for about 10 minutes, stirring often, until the sugar has melted and the grapes have softened. Transfer the mixture to the blender and puree it well, then press it through a fine-meshed strainer back into the pot. Put a small white plate in the freezer. Bring the strained mixture back to a simmer and cook, stirring the whole time, until it thickens, 10 to 15 minutes. To check it, spoon a little jam onto the frozen plate, freeze it for 1 minute, and then nudge it. If it still flows, continue cooking and check again every 2 minutes or so, until it sets. Take it out of the pot right away and scrape it into a medium mixing bowl, then cool it over an ice bath or in the refrigerator. After it has chilled, keep it in an airtight container for up to 2 weeks.
2. For the bars: Put an oven rack in the center position and heat the oven to 350 degrees F. For tall, cakier bars, grease and flour an 8- by 8-inch baking dish; for a thinner batch that bakes faster, grease a 9- by 13-inch baking sheet. Fit the pan with parchment paper, leaving extra hanging over the 2 ends. Set the pan aside.
3. In a medium bowl, whisk the butter together with the sugars until the mixture is completely blended. Whisk in the eggs, then add the vanilla and peanut butter. In another medium bowl, whisk together the flour, baking powder, and peanuts. Fold the dry mixture into the batter, then spread the batter evenly in the prepared pan.
4. For a neat chevron design, spoon the jelly into a piping bag or a plastic bag, snip off the tip, and pipe several narrow lines close together over the batter. Pull a paring knife through the lines, changing direction as you go. For a looser swirl, scatter spoonfuls of jelly evenly over the top and marble them with a paring knife.
5. If using the shallow pan, bake for 20-30 minutes, rotating it 1 time midway through. If using the smaller, deeper pan, bake for at least 1 hour, rotating every 20 minutes. The bars are done when a skewer or paring knife poked into the center shows just a few crumbs clinging to it; the crumbs should be sticky, but not wet. Cool the bars completely before taking them out of the pan. For easier lifting and cleaner cuts, refrigerate them for at least 2 hours, or leave them overnight. To cut shallow bars, use the parchment overhang to lift them from the pan and move them to a cutting board, then slice with a clean chef's knife. For thicker bars, turn them out onto a cutting board, flip them upright again, and cut with a clean chef's knife.