Preheat oven to 350°F (177°C). Line the bottoms of two 8 inch round cake pans with parchment paper and grease the sides.

In a medium bowl, whisk flour, baking powder, baking soda, and salt together. Set aside.

Beat butter and sugar together in a large bowl, or the bowl of a stand mixer fitted with the beater attachment. Add vegetable oil and eggs, and mix to combine, scraping down the sides of the bowl as needed. Slowly mix in vanilla extract and milk until combined.

Stir dry ingredients into the cake batter and then pour the batter into prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in their pans for 5 minutes, and then turn out onto a wired rack to cool completely.

Preheat oven to 350°F (177°C). Spread the flour out on a parchment lined baking sheet. Bake for 5 minutes to cook the raw taste out of the flour. Let cool for a few minutes.

In a large bowl, whisk cooled flour and powdered sugar together. Using a pastry cutter, forks, or your hands, cut in cold butter into the dry ingredients. You want the butter to coat all the dry ingredients and the size to be small. We don't want big chunks on our cake.

Stir in lemon zest and vanilla extract. Store in the refrigerator until the mixture gets cold, about 1 hour.

Whip heavy whipping cream in a large bowl to stiff peaks, and set aside.

In another large bowl, mix mascarpone cheese, powdered sugar, lemon zest and juice. Gently fold in whipped cream. Chill in the refrigerator until ready to use.

Place one cake layer on a cake plate. Reserve ¾ cup of filling, and spread or pipe the rest of the filling on top of the cake.

Place the second cake layer on top. Spread the reserved cake filling all over the top and sides of the cake.

Press crumb topping all over the tops and sides of the cake. Refrigerate leftovers for up to 3 days.