6 tablespoons unsalted butter, softened, plus more for greasing the pan 1 cup all-purpose flour, plus more for dusting the pan 2 tablespoons cornstarch 1/4 teaspoon baking soda 1/4 teaspoon kosher salt 3/4 cup plus 3 tablespoons granulated sugar, divided 2 large eggs 1/4 cup plus 2 tablespoons sour cream 1 1/2 teaspoons finely grated orange zest 1/2 teaspoon finely grated lemon zest 1 teaspoon pure vanilla extract, divided 1 cup heavy cream 1 pint strawberries, hulled and sli