Preheat oven to 350 ° F
In a small mixing bowl, cream together butter and sugar
Add egg and vanilla and beat well.
In a small bowl, whisk together, flour, baking powder and salt
In mixing bowl, alternate adding flour and skim milk, a little at a time, mixing in between additions Continue until mixed thoroughly. mixing well
Grease a 9 inch round cake pan
Pour mixture into the pie plate and bake on center rack in oven for 20-25 minutes.
Once baked ( check to make sure a toothpickl comes out clean), let cool on a wire rack.
Once cooled, slice horizontally and then cut into 8 trianglular pieces (like a pie)