In medium bowl stir together flour, baking powder and salt. In large bowl cream butter, 1/2 cup granulated sugar, and vanilla extract. (Approximately 2 to 3 minutes on speed 3) Add the egg and beat well. Gradually beat in flour mixture. Chill dough for one hour only.
You can also add jam in before baking or after baking without melting the jam, depending upon personal preference. I found that melted jam makes for a pretty presentation and is easier to stack.
Note: Over time the white icing will be tinted by the jam.