Butter and flour a 9-inch round cake pan with 2-inch sides.
In a heavy-bottomed 1-quart saucepan, stir the water and 1 cup sugar together and set over medium-high heat. Bring to a boil for about 5 minutes. Reduce heat to a simmer and continue cooking for 15 minutes, until you see it turning amber. Give the pan a swirl and cook another 5 minutes until a medium amber. Watch carefully so it doesn't overcook and burn. Total time for sugar is about 25 minutes.
Carefully pour hot caramel into cake pan, tilting the cake pan back and forth to coat bottom and sides. Set aside to cool. It will begin to harden.
Prepare pineapple, plums and cherries. Arrang 4 or 5 pineapple rings on top of the firm caramel. Place plums and cherries around pineapple rings (put a cherry into each pineapple hole).
Preheat oven to 350F.
For the cake, in a large bowl with an electric mixer on high speed, cream the butter and sugar until fluffy, about 2 minutes. Beat in the eggs, one at a time, mixing well after each addition.
Sift together the flour, baking powder and salt in a separate bowl. With mixer on medium speed, incorporate dry ingredients in increments, alternating with the orange juice and milk. Mix for 1 minute until the batter is fluffy.
Scrape the batter into the cake pan over the fruit. Spread evenly. Bake 45-50 minutes, until golden and a toothpick inserted in center comes out clean.
Cool slightly on a wire rack and then carefully invert onto a serving plate while still fairly hot. Should a piece of fruit stick to pan, just remove it and place it in it's proper place on the cake.