Preheat oven to 350 degrees. Drain pineapple reserving syrup. Halve pineapple slices. Melt butter in a 8x8x2-inch pan. Add brown sugar and 1 tablespoon of the reserved pineapple syrup. Add water to remaining syrup to make 1/2 cup. Arrange pineapple in bottom of pan. Place cherry half in center of each slice.
Cream together shortening and sugar till light. Add egg and vanilla; beat till fluffy. Sift together dry ingredients; add alternately with the 1/2 cup reserved pineapple syrup, beating after each addition. Spread over pineapple.
Bake at 350 degrees for 40 to 45 minutes. Cool 5 minutes; invert on plate. Serve warm.