Preheat oven to 350°F Liberally butter two 9x5 loaf pans, or one 9" tube pan. Add the flour and coat all surfaces (if using loaf pans, simply place one on top of the other and shake vigorously). Discard any excess flour.
Warm the butter to 65-70F (about 3 hours at room temperature). Place sugar and butter in the work bowl of a stand mixer fitted with the paddle attachment (placing the butter on top of the sugar helps keep it from flying all over your kitchen). Mix on medium for a full 5 minutes.
With the mixer turned down to low, add eggs one at a time, waiting 20-30 seconds after each addition, until the egg is fully incorporated and emulsified before adding the next. Add vanilla and salt.
With the mixer still on low, add 1/3 of the flour. Mix until the flour is completely incorporated. Scrape down the sides of the bowl and add the next 1/3 of the flour. When that's fully incorporated, scrape down again and add the last of the flour. When fully incorporated, scrape down a third time, then beat on medium for 30 seconds.
Using a scale, pour 2 lbs of batter into each loaf pan (or pour the whole thing into the tube pan). Smooth the top lightly; it doesn't need to be perfect. Bake about 1 hour, until the internal temperature is 210F and the cakes are golden-brown.
Place the cakes, in their pans, on a cooling rack for 10 minutes. Remove from pans and place bake on rack for at least another 10 minutes. Store loosely wrapped in a towel at room temperature for up to 3 days, or slice and freeze for up to 3 months. (It's very good toasted, right out of the freezer; one cycle thaws, and another toasts.).