Heat oven to 325° F. Butter a 9-by-5-inch loaf pan, line the bottom with parchment, butter again, and dust with flour, tapping out the excess.
Using an electric mixer, beat the butter, sugar, vanilla, and salt on medium until fluffy and pale, at least 5 minutes. Beat in the eggs one at a time, scraping down the sides of the bowl as necessary. Beat in the sour cream until smooth.
Reduce mixer speed to low. Add the flour and mix just until combined (do not overmix). Transfer the batter to the prepared pan, smoothing the top, and bake until the top is golden brown and domed and a toothpick inserted in the center comes out clean, about 1 hour and 15 minutes. Cool the cake in the pan for 20 minutes, then turn out onto a rack to cool completely.