Preheat the oven to 325° F.
Generously butter an 8 1/2 x 4 1/2 – inch loaf pan and set aside.
Sift together the flour and baking powder and set aside.
Put the sugar and the chopped vanilla bean, if using, in the bowl of a food processor fitted with the metal blade and pulse until the vanilla bean is finely ground. Sift through a fine-mesh sieve and return the sugar mixture to the food processor. If not using the vanilla bean, just put the sugar in the processor.
Add the butter and salt and process until light and fluffy, about 2 minutes, scraping down the sides and bottom of the bowl sometimes. Add the condensed milk and pulse until well incorporated, about 15 times, scraping down the sides of the bowl once.
Add the sifted dry ingredients and pulse until no traces of flour remain, about 10 times. Add the eggs and pulse just until combined, about 5 times. Scrape down the sides and bottom of the bowl, add the vanilla extract, if using, and finish mixing by hand to fully incorporate the eggs.
Transfer the batter to the prepared loaf pan. Bake until the top is dark golden brown and a tester inserted in the center comes out clean, 65-75 minutes. Cool fully in the loaf pan on a rack, then unmold