1. Preheat oven to 350°F (176°C) and prepare three 8 inch cake pans with non-stick baking spray and parchment paper in the bottom. These cakes can have a tendency to stick to the pans a bit, so I strongly recommend the parchment paper in the bottom.
2. Add the flour, sugar, baking powder and salt to a large mixer bowl and combine. Set aside.
3. Add the milk, vegetable oil, vanilla extract and eggs to a medium sized bowl and combine.
4. Add the wet ingredients to the dry ingredients and beat until well combined.
5. Slowly add the water to the batter and mix on low speed until well combined. Scrape down the sides of the bowl as needed to make sure everything is well combined.
6. Divide the batter evenly between the prepared cake pans and bake for 24-28 minutes, or until a toothpick comes out with a few moist crumbs.
7. Remove the cakes from oven and allow to cool for 2-3 minutes, then remove to a cooling rack to finish cooling. These cakes can have a tendency to stick to the pans a bit so jiggle them a bit to loosen from the sides of the pan before turning the cakes out to cool.
8. To make the berry topping, add the berries and water to a food processor and puree until smooth. You should end up with about 2/3 cup puree.
9. Combine the sugar and cornstarch in a medium saucepan. Stir in the berry puree.
10. Cook over medium heat, stirring consistently until mixture thickens and comes to a boil, about 8-10 minutes.
11. Allow to boil for 1 minute, then remove from heat. Refrigerate and allow to cool completely.
12. Add the heavy whipping cream, powdered sugar and vanilla extract to a large mixer bowl and whip on high speed until soft peaks form.
13. Add the mascarpone cheese to the whipped cream and whip until stiff peaks form. It will happen fairly quickly. Set whipped frosting in the refrigerator.
14. To assemble the cake, use a large serrated knife to remove the domes from the top of the cakes.
15. Place the first layer of cake on a serving plate or a cardboard cake round. Pipe a dam of frosting around the outside of the cake. I use Ateco tip 808 for the dam so that it’s tall.
16. Spread half of the berry filling evenly on top of the cake layer, inside the dam. It should fill the dam about half way full.
17. Add some additional mascarpone frosting to the top of the berry filling and spread into an even layer to fill in the remaining dam space.
18. Add the second layer of cake and repeat the filling layer with the remaining berry filling and additional mascarpone frosting.
19. Add the final layer of cake on top, then smooth out the frosting around the sides of the cake.
20. Frost the outside of the cake, then use an icing decorator (I use this one) to add a striped pattern to the sides.
21. Finish off the cake with some swirls of frosting and fresh berries.
22. Refrigerate cake until ready to serve. Cake is best for 2-3 days.