2 sticks (1 cup) unsalted butter, melted
1 3/4 cups (350 grams) dark brown sugar
2 large eggs
1 large egg yolk
1 teaspoon vanilla
1/4 teaspoon salt
2 cups (254 grams) all-purpose flour
1 cup cookie butter
2/3 cup sweetened condensed milk
- Preheat oven to 350 degrees F. Line an 8 x 8" baking pan with foil and lightly spray with nonstick cooking spray.
- In a large bowl combine the hot melted butter and sugar with a rubber spatula. Let cool. Add the eggs, egg yolk, and vanilla and stir until combined. Stir in the salt and flour.
- Spread half the batter evenly into the prepared pan. Bake for 15 minutes, or until it just begins to set. Keep oven at 350°F.
- In a heatproof container, microwave the cookie butter and condensed milk in 20-second bursts, stirring between bursts, until warmed through and well combined.
- Spread the cookie butter mixture over the par-baked blondie layer in one even layer. Use your palms to flatten pieces of the cookie butter mixture to layer over the blondie if needed. Spread the remaining blondie batter over the cookie butter layer until it’s completely covered.
- Return to the 350°F oven and bake for another 30 minutes, or until golden brown and set. Let cool completely before chopping into bars with a big sharp knife. Wipe the blade with hot water for cleaner slices.