Combine the yeast, water, sugar, and butter in the bowl of an electric mixer fitted with a dough hook. Beat for 1 minute on low speed to dissolve the yeast. Let sit until the mixture begins to foam. If it doesn’t foam, the yeast is no longer active and must be replaced. Add the egg and beat at low speed for 1 minute. Add both flours and the salt. Beat at low speed until the flour is fully incorporated, about 1 minute. Then beat at medium speed until the mixture forms a ball, leaves the sides of the bowl, and climbs up the dough hook.
Remove the dough from the bowl. Using your hands, form the dough into a smooth ball. Lightly grease a bowl with the oil. Place the dough in the bowl and turn to oil all sides. Cover with plastic wrap and set aside in a warm, draft-free place until doubled in size, about 2 hours.
Punch the dough down and put into a lightly greased 9 1/4 X 5 1/4 X 2 3/4-inch loaf pan. Cover it with plastic wrap and set aside in a warm, draft-free place until almost doubled in size, about 1 hour.
Preheat the oven to 350ºF.
Bake until golden brown, about 45 minutes. Remove from the oven and let stand for about 5 minutes. Turn onto a wire rack and cool. Cut into 1/4-inch-thick slices and remove the crusts. Cut each slice diagonally into two triangles. Place them on a baking sheet and lightly toast in the oven.
Yield: 1 loaf