Sift flour, baking powder and salt together. Cream butter until soft and gradually blend in sugar, creaming until fluffy. Add eggs and beat vigorously until light and fluffy. Add vanilla; stirring thoroughly. Add flour mixture and milk alternately in 3 or 4 portions, beginning and ending with flour and beating until smooth. Pour into two round 8" greased layer pans lined with waxed paper. Bake at 350°F for 25-30 minutes. Cool; spread partridgeberry jam between layers.