Make the Vanilla Cake

1. Preheat the oven to 350°F (176°C). Grease a 9×13 cake pan.
2. Combine the flour, baking soda, baking powder and salt in a medium sized bowl. Set aside.
3. Beat the butter and sugar in a large bowl on medium speed about 2 minutes, until light and fluffy. Scrape down the sides of the bowl.
4. Add the egg whites and vanilla and beat on medium speed until well combined and smooth.
5. Add about a third of the flour mixture to the batter and beat on medium speed until incorporated.
6. Add about half of the milk and beat on medium speed until incorporated.
7. Add another third of the flour mixture and beat until incorporated, scraping down the sides of the bowl as needed.
8. Add the remaining milk and beat on medium speed until incorporated.
9. Add the remaining flour mixture and beat until well combined, scraping down the sides of the bowl as needed.
10. Bake the cake for 35-40 minutes, or until a toothpick inserted in the center comes out clean. The cake will be browned on top.
11. When the cake is done, set aside to cool.

Make the Strawberry Sauce

1. To make the strawberry sauce, add the strawberry puree, sugar and vanilla extract to a medium saucepan. Cook over medium heat until it begins to boil, stirring occasionally.
2. Allow sauce to boil for one minutes, then remove from heat and seat aside to cool.

Make the Whipped Cream & Assemble the Trifle

1. When everything has cooled, make the whipped cream. Add the heavy whipping cream, powdered sugar and vanilla extract to a large mixer bowl and whip on high speed until stiff peaks form.
2. To layer everything in the trifle dish, add a layer of cake on the bottom, then about half of the chopped strawberries, about half of the strawberry sauce, then about half of the whipped cream.
3. Add a second layer of cake, strawberries and strawberry sauce, then pipe the remaining whipped cream on top in swirls. Add a few additional strawberries on top as decoration.