Ingredients

1 cup unsalted butter (melted and slightly cooled)

1 1/4 cups light brown sugar (packed)

1/2 cup granulated sugar

2 large eggs (room temperature)

2 teaspoons vanilla extract

2 1/4 cups all-purpose flour

1 teaspoon cream of tartar

1/2 teaspoon baking soda

1/2 teaspoon salt

1/3 cup granulated sugar (for the cinnamon swirl)

1 tablespoon ground cinnamon

2 tablespoons unsalted butter (melted for swirl)

2 tablespoons granulated sugar (mixed with 1/2 teaspoon ground cinnamon for topping)

Instructions

Step 1: Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking dish. Line it with parchment paper, leaving an overhang on the sides for easy removal.

Step 2: In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth. Add the eggs and vanilla extract, whisking until fully incorporated.

Step 3: In a separate bowl, sift together the flour, cream of tartar, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, stirring until just combined.

Step 4: In a small bowl, mix the granulated sugar and cinnamon for the swirl. Stir in the melted butter until the mixture resembles wet sand.

Step 5: Spread half of the blondie batter evenly into the prepared baking dish. Sprinkle the cinnamon-sugar mixture over the batter evenly. Dollop the remaining batter on top and gently spread to cover.

Step 6: Using a butter knife, create gentle swirls in the batter to incorporate the cinnamon mixture without fully blending it in.

Step 7: Optionally, sprinkle some of the cinnamon-sugar topping over the surface for added crunch and flavor.

Step 8: Bake in the preheated oven for 30–35 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with a few moist crumbs.

Step 9: Allow to cool in the pan for 20 minutes. Lift the blondies out using the parchment paper, transfer to a cutting board, and slice into squares.

Tips & Variations

For extra softness, slightly underbake the blondies by a couple of minutes—remember they will continue to cook as they cool.

Swap out the cinnamon swirl for a mix of chopped nuts and chocolate chips for a crunchy, chocolaty surprise.

If you don’t have cream of tartar, you can substitute with an equal amount of baking powder.

FAQs

Can I use salted butter instead of unsalted?

Yes, but reduce the added salt in the recipe to 1/4 teaspoon to avoid over-salting the blondies.

How do I know when my blondies are perfectly baked?

The edges should be golden brown while the center remains slightly soft. A toothpick inserted into the middle should come out with a few moist crumbs but not wet batter.