Do not worry if the cheesecake sinks and cracks while it cools. The stewed fruit will conceal any imperfections.
Preheat oven to 350 degrees. In the bowl of an electric mixer fitted with the paddle attachment, cream butter and 1/2 cup plus 2 tablespoons sugar until light. Add flour, cornmeal, and salt, and mix until well combined. Press mixture onto the bottom and 3/4 of the way up sides of a 10-by-3-inch springform pan to form a neat crust. Place in the oven, and bake until lightly golden, 20 to 25 minutes. Remove pan from oven, and place on a wire rack. Gently press sides of crust back into place if necessary. Let cool to room temperature.
Reduce oven to 325 degrees. In the bowl of an electric mixer fitted with the paddle attachment, beat cream cheese, mascarpone, and remaining 1 1/4 cups sugar on low speed until smooth and well combined. Add eggs and egg yolk, one at a time, beating on low speed after each addition until combined, scraping down sides of bowl with a rubber spatula as necessary.
Add cream, vanilla extract, and orange and lemon zests; beat just until combined. Do not overbeat. Pour mixture into cooled shell; place in oven; bake until set but still wobbly in center, 65 to 70 minutes. Turn oven off, and allow cheesecake to sit in the oven 1 hour more. Remove cheesecake from oven, and place on a wire rack to cool. When completely cool, chill at least 2 hours or overnight. Remove outside ring of springform pan.
Combine stewed rhubarb with raspberries. Spoon fruit over cheesecake immediately before serving.