Make the Cake

1. Preheat oven to 350°F (176°C) and prepare a 9×13 inch cake pan with non-stick baking spray.
2. Combine the flour, baking powder, baking soda and salt in a medium-sized bowl and set aside.
3. Add the butter, oil, sugar and vanilla extract to a large mixer bowl and beat together until light in color and fluffy, about 2-3 minutes. Do not skimp on the creaming time.
4. Add the eggs one at a time, mixing until mostly combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Add half of the dry ingredients to the batter and mix until mostly combined.
6. Combine the milk, 1/2 a cup of lemon juice, and lemon zest, then slowly add the mixture to the batter and mix until well combined.
7. Add the remaining dry ingredients and mix until well combined and smooth. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Do not over mix the batter.
8. Pour the batter into the prepared cake pan and bake for 20-25 minutes, or until a toothpick comes out clean.
9. Remove the cake from the oven and poke holes all over the top of the cake. I use a knife sharpener, but the end of the handle of a wooden spoon or spatula would work too.
10. Combine the sweetened condensed milk and remaining 1/2 cup of lemon juice and pour over the top of the warm cake, allowing it to soak into the holes. If a little bit remains on top of the cake, that’s ok. Let cake cool completely.

Make the Frosting

1. Place the heavy whipping cream, powdered sugar and vanilla extract into a large mixer bowl. Whip on high speed until soft peaks form.
2. Add the mascarpone cheese and continue whipping. Start on low speed to let it begin to incorporate, then turn it up to high speed until stiff peaks form, which should happen quickly.
3. Pipe or spread the whipped cream onto the cake.
4. Refrigerate the cake until ready to serve.