In medium bowl, combine flour, baking powder, cinnamon and salt; set aside. In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add eggs, one at a time, and vanilla; mix well. Alternately add flour mixture and applesauce to butter mixture. Spread about 1/2 of cake batter so that it reaches the first horizontal line inside the pan. Sprinkle diced apples evenly over batter. Top with remaining batter, smoothing out the top.