Preheat oven to 325 degrees F. Generously grease and flour 2 - 9"x5" loaf pans and set aside.
Sift together the flour and baking powder, set aside.
If you are using the vanilla bean, place it and the sugar in the bowl of a food processor fitted with the metal blade and pulse until the vanilla bean is finely ground. Sift the sugar and vanilla bean through a fine-mesh sieve into the bowl of a stand mixer fitted with the paddle attachment, add the butter and cream until light and fluffy (about 2 minutes).
If you are not using the vanilla bean, simply place the sugar and butter in the bowl of a stand mixer fitted with the paddle attachment and cream until light and fluffy (about 2 minutes).
Add the condensed milk and dulce de leche and beat until well combined scraping down the bowl as necessary.
Add the sifted dry ingredients and mix on low speed until no traces of flour remain.
Add the eggs and mix just until combined.
Add the vanilla extract and finish mixing by hand to incorporate the vanilla and finish incorporating the eggs.
Split the batter evenly between the prepared pans and place in the oven. Bake until the top is dark golden brown and a tester comes out with a few moist crumbs (this may take 45 minutes to an hour) Cool completely in the pans before un-molding.
