• 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 beat until light and fluffy, scraping down the sides of bowl as needed, about 2 minutes. Add eggs, 1 at a time, beating until incorporated after each addition, about 30 seconds. Whisk together flour, cornstarch, baking powder, and salt in a medium bowl until combined. Add flour mixture to butter mixture in 3 additions, alternating alternately with the milk, starting and ending with the flour mixture, and beat until combined after each addition. Turn dough out onto a floured work surface and turn to coat dough. Knead dough 2 or 3 times. Divide dough into 5 equal pieces and shape each piece into a ball.

Working with 1 ball at a time, roll dough into a 7-inch circle. Place dough circles on 2 large rimmed baking sheets lined with parchment paper (I fit 3 circles on 1 sheet and 2 on the other). Chill dough circles, uncovered, for 1 hour. Preheat oven to 375 degrees F (190 degrees C). Prick each dough circle lightly with a fork. Bake in the preheated oven until browned on bottom and light browned around the edges, 15 to 18 minutes. (If baking in 2 batches, keep second batch refrigerated while first batch bakes.) Cool cake layers completely on a wire rack, about 30 minutes. Spoon dulce de leche into a medium bowl. Beat cream with an electric mixer on medium-high speed until stiff peaks form, about 6 minutes. Gently stir half of cream mixture into dulce de leche until combined. Gently fold remaining cream into dulce de leche mixture until combined. Spread 1/3 cup of the dulce de leche mixture onto 1 cake layer, spreading to edges. Place onto a serving platter with dulce de leche mixture facing up. Repeat process with the next 3 cake layers (this is easier to spread on cake layers before placing on platter). Spread remaining 2/3 cup dulce de leche mixture onto fifth cake layer and place on top. Let stand 1 hour. Dust top of cake with powdered sugar and serve. Cover any leftovers with plastic wrap and store in refrigerator up to 1 day.