Cake

1 cup plus 2 tablespoons all-purpose flour
2 tablespoons cornstarch
1 1/4 teaspoons baking powder
1/8 teaspoon salt
3/4 cup granulated sugar
2 large eggs, at room temperature
1 1/4 teaspoons pure vanilla extract
4 tablespoons unsalted butter, melted
1/4 cup vegetable oil
1/2 cup milk, at room temperature

Frosting and Topping

6 tablespoons unsalted butter, softened
2 cups confectioners' sugar, sifted
1/2 teaspoon pure vanilla extract
Pinch of salt
2 tablespoons milk or heavy cream
Strawberry jam