For the topping: Grease bottom and sides of 9 x 3-inch round cake pan. Melt 4 tbsp butter in medium saucepan over medium heat; add brown sugar and cook, stirring occasionally, until mixture is foamy and pale, 3 to 4 minutes. (Next time I would just do this step in the microwave.)
Pour mixture into prepared cake pan; swirl pan to distribute evenly. Arrange fruit slices in concentric circles over topping; set aside.
For the cake: Adjust oven rack to lower-middle position and heat oven to 350º F. Whisk the flour, baking powder, cornmeal (I would omit next time), and salt together in medium bowl; set aside.
Cream butter in large bowl with electric mixer at medium speed. Gradually add 1 cup sugar; continue beating until light and fluffy, about 2 minutes. Beat in yolks and vanilla (scraping the sides of the bowl if necessary); reduce speed to low and add dry mixture and milk, alternately in three or four batches, beginning and ending with dry ingredients, until batter is just smooth.
Beat egg whites in large bowl at low speed until frothy. Increase speed to medium-high; beat to soft peaks. Gradually add 2 tbsp sugar; continue to beat to stiff peaks.
Fold one-quarter of beaten egg whites into batter with large rubber spatula to lighten. Fold in remaining whites until no white streaks remain.
Gently pour batter into pan and spread evenly on top of fruit, being careful not to disperse fruit. Bake until top is golden and toothpick inserted into cake center (but not into fruit, which remains gooey) comes out clean, 60 to 65 minutes.
Rest cake on rack for 2 minutes. Slide a paring knife around the edge of the cake to loosen it from the pan. Place a serving platter over the pan and hold tightly. Invert the cake onto the platter. Carefully remove the cake pan. If any fruit sticks to the pan bottom, remove and position on top of cake.