Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, combine the melted butter and brown sugar. Whisk them together until smooth and well blended.
Add in the eggs one at a time, mixing well after each addition, and then stir in the vanilla extract until fully incorporated.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon.
Gradually add the dry ingredients to the wet mixture. Stir until just combined, being careful not to overmix.
Pour the batter into your prepared baking pan and spread it evenly.
In a small bowl, mix the granulated sugar with an additional tablespoon of cinnamon. Sprinkle this cinnamon sugar mixture generously over the top of the uncooked batter.
Bake in the preheated oven for 20-25 minutes, or until the edges are golden and a toothpick inserted into the center comes out clean.
Allow the blondies to cool in the pan for at least 10 minutes before slicing into squares.
Notes
Serve warm with a scoop of vanilla ice cream or drizzle with icing for added sweetness.