This is an old time classic, but I am always surprised how many people ask me for this recipe. And bar cookies are just so much easier to make than any others.
Preheat oven to 350 deg. In a medium bowl, cream 1 c. (2 sticks) butter and 1/2 c. 10X sugar. Add 2 c. flour and stir with a wooden spoon until well combined. Pat evenly into a 13 x 9 pan and bake for 20 minutes.
In a blender, combine 4 eggs, 1 3/4 c. granulated sugar, 1/3 c. lemon juice, 1/2 tsp. baking powder and 1/3 c. flour. Blend for 5 seconds. Scrape down and blend again for another 5 seconds. Pour over partially baked crust. Bake for 25 more minutes or until golden brown. Cool completely. Sprinkle with confectioner's sugar and cut into bars or squares.