Preheat oven to 350°F. Lightly butter and flour a 4 1/2-by-8 1/2-inch loaf pan. In a large bowl, using an electric mixer, beat butter and sugar on medium-high until very light and fluffy, 7 minutes. Scrape down bowl and beat 1 minute more. Add vanilla, then gradually add eggs, beating well and scraping down bowl as needed. With mixer on low, add salt, then gradually add flour, beating well to combine and scraping down bowl as needed.