Grease and lightly flour a 9x1 1/2 inch or 8x 1/2 inch round baking pan. In a small mixing bowl stir together flour, baking powder and salt. Set pan and flour mixture aside.
In a medium mixing bowl beat egg with an electric mixer on high speed for 3 to 4 minutes or until thick and lemon-colored. Gradually add sugar, beating on medium speed 4 to 5 minutes or until sugar is almost dissolved. Add flour mixture. Beat low to medium speed "just until combined".
In a small saucepan heat the milk and butter just until butter melts. Stir warm milk mixture into egg mixture. Pour batter into prepared pan; spread evenly.
Bake about 18 minutes or until cake top springs back when touched. Cool cake in pan on a wire rack for 10 minutes. Loosen cake from sides of pan. Invert cake onto a wire rack and cool completely.
To make ahead, wrap cooled cake in freezer wrap or foil and freeze for up to 1 month. Thaw at room temperature before using.