Preheat the oven to 350°F. Prepare three 8-inch round baking pans, line the bottom with parchment paper, and grease the sides.

In a large mixing bowl, combine the sugar, vegetable oil, eggs, and vanilla extract. Beat on medium speed until well incorporated, about 2 minutes.

Mix in the sour cream and beat until well combined.

Combine the dry ingredients in a separate bowl. Add half of the dry ingredients and beat on low speed while pouring in half of the milk.

Add the remaining dry ingredients, mixing on low while pouring in the remaining milk, until all ingredients are well combined.

Divide the batter evenly between the pans, about 1 ⅔ cups per pan. Bake at 350°F for 20-23 minutes.

Test for doneness with a toothpick. Remove from oven and allow to cool completely.

Chop and puree the strawberries.

In a saucepan, combine the flour and sugar, then add the pureed strawberries and lemon juice, stirring well.

Cook over medium heat until boiling, then reduce heat and simmer for 5-10 minutes until thickened.

Allow the puree to cool completely.

Chill a mixing bowl and whisk attachment in the freezer for 5-10 minutes.

Beat cold mascarpone and gradually pour in heavy cream.

Increase speed to high and beat until soft peaks form.

Add powdered sugar and vanilla, then beat at high speed until stiff peaks form.

Level the top of the cake using a cake leveler.

Pipe a thick border of frosting around the edges of the bottom cake layer.

Spread half of the strawberry mixture over the cake.

Pipe a thin layer of frosting over the strawberry sauce.

Add the second layer of cake and repeat using all of the remaining strawberry sauce.

Fill the gaps between layers with frosting and create a crumb coat.

Frost the top and sides of the cake, smoothing with an icing smoother.

Pipe flourishes on top using the remaining frosting and garnish with strawberries.