Insert metal blade.
Place flour in work bowl; process for 5 seconds to sift.
With motor running, drop butter, one chunk at a time, through feed tube.
Continue processing until soft and smooth.
Add sugar to work bowl and process continuously (stopping to scrape bowl once or twice) until mixture is light and fluffy.
Place eggs and vanilla in a measuring cup; with motor running, pour slowly through feed tube and continue processing (stopping to scrape bowl once or twice) until creamy.
Add flour to work bowl and process, using on-off pulses, just until evenly combined.
Pour into a greased 5 by 9-inch loaf pan.
Bake in a 325° oven until a wooden pick inserted in center comes out clean (about 1 hour).
Let cool in pan for 5 minutes; then turn out onto a rack and let cool completely.