Position rack in center of oven

Butter sides and bottom of 9x13 pan

Line bottom of pan w/parchment and lightly butter

In med. bowl sift together flour, cocoa, baking powder and salt

Seperate eggs in med bowl, yolks in large bowl

Beat yolks with3\4 cup sugar @ med. speed til pale and creamy, about two minutes

Add milk and vanilla--beat till combined (about one minute)