Preheat the oven to 325° F. Generously butter an 8 1/2 x 4 1/2 – inch loaf pan and set aside. Combine the flour, salt, and baking soda in a small bowl and whisk together. Set aside.
Cream the butter and sugar in the bowl of a food processor and pulse until light and fluffy, about 2 minutes, scraping down the sides and bottom of the bowl occasionally. Add the condensed milk and pulse until well incorporated, about 15 times.
Add the dry ingredients and pulse until no traces of flour remain. Mix in the eggs and pulse just until combined, about 2-3 minutes. Scrape down the sides and bottom of the bowl, add the vanilla extract, and finish mixing until well incorporated.
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 completely in the loaf pan on a rack, then unmold.