Melt butter in a 9" square pan. Stir in brown sugar and mix well in the pan. Arrange pineapple slices in the bottom of the pan. Place 1/2 a cherry in the middle of each pineapple ring.
Drain the pineapple, reserving syrup. Add water to remaining syrup to make 1/2 cup.
Cream together shortening and white sugar until light. Add egg and vanilla. Beat until fluffy. Add dry ingredients plus 1/2 cup reserved pineapple syrup. Beat until all is well mixed.
Preheat oven to 350ºF.
Bake for 40 to 45 minutes. Cool for 5 minutes in the pan then invert the cake on to a plate. Great served warm with a dollop of whipped cream.