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.

Mix in the sour cream and beat until well combined.

Combine the dry ingredients in a separate bowl. Add half the dry ingredients and half of the milk, mix until flour starts to incorporate.

Add remaining dry ingredients, while pouring in remaining milk, beating until combined.

Divide batter evenly between the pans and bake at 350°F for 20-23 minutes, rotating halfway through.

Test for doneness with a toothpick. Let cool completely.

Chop and puree the strawberries.

In a saucepan, combine the flour and sugar, then add the pureed strawberries and lemon juice. Cook until it boils, stirring frequently.

Reduce heat and simmer for 5-10 minutes until thickened.

Allow to cool completely.

Chill mixing bowl and whisk attachment for 5 to 10 minutes.

Beat the cold mascarpone, then slowly add heavy cream until it becomes liquid.

Increase speed and beat until soft peaks form.

Add powdered sugar and vanilla, beating until stiff peaks form.

Cut domes off the cake layers and place one on the board with a dollop of frosting.

Pipe a border of frosting, then spread half of the strawberry mixture inside.

Pipe another layer of frosting, add the second layer of cake, and repeat.

Add the final layer and crumb coat with frosting.

Frost top and sides, smoothing with an offset spatula.

Decorate the top with remaining frosting and garnish with strawberries.