Preheat oven to 350°F Beat butter and sugar in a large bowl at medium speed until creamy. Add flour and salt; mix on low until blended. Spread evenly in bottom of greased 8"x8" baking pan. Bake 15 to 20 minutes until crust is golden.
For filling: Beat eggs and sugar in bowl at medium speed. Add in butter, corn syrup, flour, buttermilk, vanilla, and lemon peel, if using; beat until smooth. Pour filling over baked crust.
Bake 20-25 minutes until edges just begin to brown and filling is set. Cool completely. Sprinkle with powdered sugar and cut into 12 bars.