Line an 8x8-inch baking dish with parchment paper and set aside.
Preheat your oven to 350°F (175°C).
In a large bowl, combine melted (and cooled) butter with both brown sugar and granulated sugar. Stir until thoroughly combined.
Add the eggs and mix until smooth.
Gradually incorporate the baking soda and flour, stirring until no flour clumps remain.
Pour the batter into the prepared baking dish, spreading it evenly.
In a small bowl, mix the cinnamon and sugar for the topping, then sprinkle it generously over the batter.
Bake for 35-40 minutes, or until the edges are golden brown and the center remains slightly soft.
Remove from the oven and allow the blondies to cool for 45 minutes to 1 hour.
While cooling, prepare the glaze by whisking the ingredients together until smooth and runny.
Drizzle the glaze over the cooled blondies and let it set for 15-30 minutes.
Carefully lift the blondies out of the pan using the parchment paper. For even portions, cut into 16 squares by making four cuts in one direction, then turning and cutting four more times.