In a throwback to your favorite childhood lunchbox item, we added luscious swirls of grape jelly and extra peanut butter to the top of our peanut butter-rich batter. Swap out the grape jelly for your favorite flavor. 

• 2 cups (440 grams) firmly packed light brown sugar
• 1 cup (227 grams) unsalted butter, melted and cooled
• 1 cup (256 grams) creamy peanut butter*, melted and divided
• 1 teaspoon (5 grams) baking powder
• ½ teaspoon (1.5 grams) kosher salt
• 2 large eggs (100 grams), room temperature
• 2 teaspoons (8 grams) vanilla extract
• 2½ cups (313 grams) all-purpose flour
• ½ cup (160 grams) grape jelly

1. Preheat oven to 350°F (180°C). Line a 13×9-inch baking pan with parchment paper, letting excess extend over sides of pan.

2. In a large bowl, whisk together brown sugar, melted butter, ½ cup (128 grams) melted peanut butter, baking powder, and kosher salt until combined. Add eggs, one at a time, whisking well after each addition. Whisk in vanilla. Stir in flour just until combined. Spread batter into prepared pan.

3. In separate heatproof bowls, microwave remaining ½ cup (128 grams) peanut butter and grape jelly in 5-second intervals until warm. (Do not heat either for more than 15 seconds. You do not want them to be liquid.) Drop slightly warmed peanut butter and jelly in alternating tablespoonfuls across the top surface of the batter, making sure to reach the edges. Using the tip of a butter knife or small offset spatula, swirl peanut butter and jelly together to create marbled effect. (It is fine to pull through top of batter.) Bake for 35 to 40 minutes. Let cool completely in pan on wire rack. Using excess parchment as handles, remove from pan, and cut into 12 blondies. Store in an airtight container for up to 3 days.

*We used Jif Creamy Peanut Butter, but you can also use crunchy peanut butter for additional texture.