Preheat oven to 350F degrees. Line a 9x9, 11x7, or 9x13 inch baking pan with aluminum foil, leaving enough overhang on the sides to easily pull the blondies out of the pan and cut. I suggest using an 11x7 baking pan - that is what I have been using and the blondies are nice and thick.

In small bowl, combine flour, baking powder, and salt. Set aside. Using a hand or stand mixer fitted with a paddle attachment, beat the butter on high speed in a large bowl. Beat for at least 1 minute until creamy. Add sugars and beat for 2 full minutes on high speed until light and fluffy. Scrape down the sides and bottom of bowl as needed. Beat in the eggs and vanilla on high speed, scraping down the sides and bottom of the bowl as needed. On low speed, beat in dry ingredients until just combined. With a large wooden spoon or rubber spatula, fold in the white chocolate chips.

Spoon half the batter into pan. It will be a relatively thin layer, but try to spread it across the pan evenly. Combine the cinnamon and sugar and sprinkle on top of them bottom layer, reserving 1 Tablespoon for the top. Spread the remaining batter over top. Some of the cinnamon-sugar will mix into the top layer as you spread it, which is fine. Sprinkle the top with remaining cinnamon-sugar.

For a 9x9 or 11x7 baking pan, bake for 30-35 minutes or until golden brown and a toothpick inserted in the center comes out clean. For a 9x13, bake 22-26 minutes or until golden brown and toothpick inserted in center comes out clean. Cool completely for about 1 hour.

Make ahead tip: These bars can be made 3 days in advance and kept in an airtight container at room temperature until ready to serve. Bars freeze well, up to 3 months. Simply thaw overnight in the refrigerator and bring to room temperature before serving. Leftover bars can be stored in an airtight container in the refrigerator or at room temperature for up to 1 week.