Preheat the oven to 350 degrees F. Lightly grease a 9-by-13-inch baking pan with nonstick spray and line with parchment, leaving a 2-inch overhang on the long sides for lifting out the finished bars.
In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl with a handheld mixer), cream the butter with 1 cup of the granulated sugar and all of the brown sugar until light and fluffy, 4 to 5 minutes.
Scrape the bowl well with a rubber spatula, then add the eggs one at a time and mix on medium speed after each addition until well combined. Beat in the vanilla.
Add the flour, baking powder and salt and pulse until they start to combine, then scrape the bowl well and mix on low speed until the dough is uniformly combined.
Scoop the dough into the prepared pan and press into an even layer. Stir the remaining 1/4 cup granulated sugar with the cinnamon in a small bowl. Sprinkle the cinnamon sugar evenly over the bars.
Bake until the edges are golden and the center is set, 25 to 30 minutes.
Let cool completely in the pan, then run a small spatula around the edge. Use the parchment overhang to carefully lift the bars out of the pan. Cut into 16 equal bars.