6 tablespoons unsalted butter, softened ⅓ cup white sugar 2 large eggs 2 ½ cups all-purpose flour, plus more for dusting ½ cup cornstarch 1 teaspoon baking powder ½ teaspoon kosher salt ½ cup whole milk 1 (13.4 ounce) can dulce de leche ½ cup heavy whipping cream ¼ cup powdered sugar, or as needed Beat butter with a stand mixer fitted with a paddle attachment on medium speed until creamy, about 2 minutes. Add sugar and…