Insert metal blade in food processor bowl. Add flour, sugar, yeast, and salt; process 10 seconds to combine. Place butter and egg in food processor. Begin processing, then slowly pour warm water through feed tube just until dough forms a ball, about 10 to 15 seconds. Continue processing for 60 seconds to knead dough. Carefully remove dough from processor bowl and place on a lightly floured surface. Cover and let rest for 10 minutes.
Form dough into a loaf and place in a lightly greased 8x4 inch loaf pan. Cover and let rise until doubled, about 45 minutes. Meanwhile, preheat oven to 375 degrees F (190 degrees C).
Bake in the preheated oven for about 30 minutes or until the top is golden brown and the bottom of the loaf sounds hollow when tapped.
