Preheat oven to 350ºF (180ºC).
Grease two 8-inch (22cm) round springform cake pans with 2 tablespoon shortening. Dust with 2 tablespoons flour, shaking off excess. Reserve.
Sift 2 ⅔ cups all-purpose flour, 2 teaspoons baking powder and ½ teaspoon salt. Reserve.
In a large mixing bowl beat soft 1 cup unsalted butter until creamy, about 1 minute.
Gradually add 1 ⅔ cups sugar, and beat for 4 minutes, until very light. Scrape down the sides of the bowl with a spatula as needed.
Add 4 eggs, one at a time, and beat until smooth between additions.
Add the dry ingredients in 3 additions, alternating with 1 cup whole milk and 2 teaspoons vanilla extract in 2 additions; you start and end with the flour mixture. Mix *just* until well integrated and smooth. Overbeating will make the cake tough.
Pour into the prepared pan and bake for about 30 minutes, or until a cake tester or toothpick inserted in the center comes out clean.
Let the pans cool on wire racks for 15 minutes. Then, remove the cakes and let them cool completely on the wire racks before filling and frosting.
You can make a 2-layer or a 4-layer cake. Cut the cake in half, trying to cut it as even as possible. To achieve this, start by using a large thin knife, and cut while rotating the cake. With each turn, the knife should go deeper, until you reach the center. At that point the cake will be completely cut in half. Spread 1 ½ cups dulce de leche on top of one half, spreading evenly.
Top with the other cake layer and press lightly. At this point, you can wrap the cake and refrigerate it for 1 day. I put them back in the cake pan, close the springform ring and wrap the whole pan.