Heat oven to 325°F (165°C). Grease and flour pan. In large mixing bowl, mix butter, powdered sugar and egg until light and fluffy. Sift together flour, cornstarch, baking powder and salt. Add to butter mixture; mix well. Spoon about 1 Tbsp of the batter into each prepared cup. Bake for 20 to 23 minutes or until light golden brown. Cool 10 minutes. Remove from pan; cool completely on rack. Place about ½ tsp of the raspberry jam in center of each cake. Lightly dust with powdered sugar, if desired. Makes 12 cakes.