Preheat oven to 350 F. Line a 13x9 baking pan with foil, spray the foil generously with cooking spray.
Whisk together flour, powdered sugar, salt, and baking powder. Drop the butter into the flour mixture and work it with your fingers until mixture resembles coarse crumbs and begins to stick together.
8.5 ounces all purpose flour, 2 ounces powdered sugar, 1/4 teaspoon salt, 1/4 teaspoon baking powder, 2/3 cup unsalted butter
Press evenly into prepared pan and bake for 15 minutes, or until lightly browned. Remove from oven and place on cooling rack.
Whisk eggs in a large bowl until lightly beaten. Add sugar and brown sugar and beat well. Whisk in the corn syrup gradually and then beat in vanilla and melted butter. Fold in 1-1/4 cups of the pecans. Pour filling over the crust in the pan, sprinkle with remaining 1/2-cup pecans.
As with all baking recipes, it's important to properly measure your flour. Too much flour can result in a dry, crumbly crust. I highly recommend using a kitchen scale and following the measurements listed here.
If you do not have a scale, use the scoop and sweep method. Aerate the flour with a spoon, then scoop it into a measuring cup until slightly overflowing. Level it off with the back end of a butter knife. Never tap your measuring cup on the counter, scoop straight from the bag, or condense the flour in the cup. Those are all sure-fire ways to end up with too much flour!