Ingredients:

  • 0.5 cup unsalted butter, melted and slightly cooled
  • 1 cup granulated sugar
  • 1 large egg, room temperature
  • 1 tablespoon vanilla extract
  • 1.5 cups all-purpose flour
  • 1 teaspoon cream of tartar
  • 0.5 teaspoon baking soda
  • 0.25 teaspoon fine sea salt
  • 2 tablespoons granulated sugar
  • 1.5 teaspoons ground cinnamon

Instructions:

  1. Preheat your oven to 350°F (175°C). Line an 8x8-inch square baking pan with parchment paper, leaving an overhang on the sides for easy removal.
  2. In a large mixing bowl, whisk together the 1/2 cup melted butter and 1 cup of granulated sugar until well combined. Add the egg and vanilla extract, whisking until the mixture is glossy and smooth.
  3. Sift the flour, cream of tartar, baking soda, and salt directly into the bowl with the wet ingredients. Use a silicone spatula to fold the ingredients together until just combined, being careful not to overmix.
  4. Press the dough evenly into the bottom of the prepared baking pan.
  5. In a small bowl, whisk together the remaining 2 tablespoons of sugar and 1.5 teaspoons of ground cinnamon. Sprinkle this mixture evenly over the top of the dough.
  6. Bake for 22–26 minutes. The bars are done when the edges are set and starting to pull away from the pan, while the center retains a very slight jiggle.