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 richness, use browned butter instead of melted butter in the batter.

Add chopped nuts like pecans or walnuts for added crunch in the blondies.

Swap the cream of tartar with an equal amount of baking powder if unavailable.

For a lighter cinnamon flavor, reduce the cinnamon in the swirl mixture by half.

Serve warm with a scoop of vanilla ice cream for a delightful dessert.

FAQs

Can I use salted butter instead of unsalted butter?

Yes, but reduce or omit any added salt in the recipe to prevent the blondies from becoming too salty.

How do I know when the blondies are done baking?

The edges should be golden brown and a toothpick inserted into the center should come out with a few moist crumbs. Avoid overbaking to keep them chewy.