How to Make It
Preheat oven to 350°.
To prepare cake, coat an 8 x 4-inch loaf pan with cooking spray; set prepared loaf pan aside.
Lightly spoon all-purpose flour into dry measuring cups; level with a knife. Combine flour, polenta, baking powder, and salt in a medium bowl, stirring with a whisk; set aside.
???,,vanilla extract and whole eggs in a small bowl, stirring well with a whisk. Combine 1 cup sugar and butter in a medium bowl; beat with mixer at medium speed until mixture is light and fluffy (about 5 minutes). Gradually add vanilla extract mixture and egg whites to sugar mixture, beating well (about 2 minutes). Gradually add flour mixture, and stir batter just until moist.
Pour cake batter into prepared pan. Bake at 350° for 1 hour or until a wooden pick inserted in center comes out clean. Cool cake in pan 10 minutes on a wire rack; remove cake from pan. Cool completely on wire rack. Cut cake into 9 equal slices.
To prepare berry topping, combine 1 tablespoon sugar, water, and thawed raspberries in a food processor or blender; process until the mixture is smooth. Strain mixture through a sieve over a bowl, pressing with the back of a spoon; discard solids. Combine raspberry sauce, strawberries, blueberries, fresh raspberries, and blackberries in a large bowl; toss gently to combine.
Prepare grill to medium-high heat.
Place cake slices on grill rack coated with cooking spray; grill 1 minute on each side or until golden brown and grill marks form. Serve grilled cake slices with berry topping.