Preheat oven to 350 degrees F. Line the bottom of two 8-inch cake pans with parchment paper rounds and spray with nonstick spray. Set aside.

Cake Batter: In a large mixing bowl with electric beaters, or bowl of a stand mixer fitted with the paddle attachment, combine the butter and the sugar. Cream together for about 3 minutes, until light and fluffy. Add vanilla and then eggs, mixing in one at a time, until combined.

With the mixer on, add sour cream, and slowly add 1/2 of the can of dulce de leche, mixing until batter becomes lighter in color.

In a separate bowl combine the flour, baking powder and salt. With the mixer on low speed, alternately add the dry mixture and the milk, starting and ending with the dry mixture.

Bake: Pour the batter into prepared cake pans and bake for about 23-25 minutes, or until a toothpick inserted in the center of the cake comes out clean (or with a few moist crumbs). Do NOT over bake or the cake will be dry. Allow to cool for a few minutes before inverting onto wire cooling racks to cool completely.

Dulce de Leche Buttercream Frosting: In a stand mixer fitted with the paddle attachment, combine the butter, powdered sugar and 1/2 can of dulce de leche and beat for several minutes, until very fluffy and smooth. Add a little milk, if needed, to thin the frosting.

Assemble: Place one cake round serving plate. Spread a thin layer of frosting over the top. Add 1/2 of the second can of dulce de leche to a small bowl and microwave for a just a few seconds, to soften it a little. Spread it on top of the cake, leaving a 1 inch border. Place the second cake round on top. Pipe a line of frosting into the crack between the two layers of cake. Frost cake completely with a very thin layer of frosting—the crumb coat. Refrigerate for 20 minutes, or freezer for 10 minutes. Remove and then add another layer of frosting over the crumb coat.

Warm the remaining 1/2 can of dulce de leche in a small bowl in the microwave for a just a few seconds to soften. Smooth dulce de leche over the top of the cake, leaving a 1-inch board. Pipe decorative frosting swirls around the outer top edge of the cake.

Sprinkle a pinch of flake salt on top of the cake, if desired.