Spray a 9x13-inch baking pan with nonstick cooking spray.
Cream together softened butter and sugar in a large mixing bowl. Add flour and salt and mix until blended. Press into the bottom of prepared pan and bake for 15 minutes.
While crust is cooking, make filling by mixing together sugar, eggs, lime zest, lime juice, and flour. Pour filling over hot crust and bake for about 25 -30 minutes or until set.
Remove from oven and dust with powdered sugar.
Cool completely and cut into squares, top with a slice of lime.
Notes
You will want to make the filling for your bars while the crust bakes alone so you can return them to the oven fairly quickly, or before the crust cools.