Spray the bottom of a 13"x9" baking pan with baking spray and line with a parchment sling.
Make the batter
Add flour, baking powder and salt to a bowl and whisk until combined.
292 g all-purpose flour, 1 ¼ teaspoon baking powder, ½ teaspoon salt
Either with an electric mixer or in the bowl of a stand mixer with the paddle attachment, beat butter on high speed for about 2-3 minutes, until creamy and light in color. Add in both sugars and beat well.
170 g butter, room temperature, 250 g sugar, 100 g brown sugar
Beat in the eggs one at a time, and then beat in the vanilla extract.
3 eggs, 1 teaspoon vanilla extract
Add the dry ingredients a little at a time into the butter mixture, until everything is incorporated.
Add the toppings
Add half of the batter to the prepared baking pan and smooth out across the bottom of the pan.
Mix together the cinnamon and sugar, and sprinkle evenly all over the batter in the pan.
1 tablespoon sugar, 1 tablespoon cinnamon
Spoon the rest of the batter on top of the cinnamon layer so that parts of the cinnamon show through.
Bake for 20 to 25 minutes. A toothpick should come out clean, or the internal temperature should read 205° F.
After the bars are completely cool, cut into squares. *Note: you can also glaze first and then cut the bars.
Mix the powdered sugar, vanilla and 1 tablespoon of the milk or cream. Add more milk or cream depending on how thick you would like the glaze to be.
125 g powdered sugar, 1-2 tablespoon milk or heavy cream, ¼ teaspoon vanilla extract
Drizzle the glaze over top of the bars and serve.
Store in an airtight container at room temperature for about 2-3 days, or freeze. For best freshness, wrap each individual bar.