Place about three cups of the 5-6 cups of whole wheat flour in the bowl of your stand-type mixer. Add the yeast. Carefully measure 2 cups room temperature (80 degrees) water. The water should feel cool to the touch. Mix the water with the flour with a dough hook for 30 seconds or until the yeast is dissolved and the ingredients begin to combine.
Add the salt, egg, sugar, and butter and continue mixing. Add most of the remaining flour and continue mixing at a medium speed for at least four minutes adding more flour as needed to reach a soft dough consistency. (It is important that the dough be mixed for at least four minutes to develop the gluten.) The dough should clear the sides of the bowl but will be soft, not firm, to the touch.
Once the dough is mixed, place it in a large greased bowl, turning once to coat both sides, and cover with plastic wrap. Refrigerate overnight or for up to three days.
On the day that you would like to bake your bread, remove the dough from the refrigerator and let it warm to room temperature--about three hours. The dough should rise to nearly double in size.
Once the dough has risen, form the loaves. Coat your hands with flour and gently form a loaf by pulling the dough around itself to create a slightly stretched skin. You may need to coat your hands several times if the dough is sticky. If necessary, pinch the seams together on the bottom of the loaf. Lay the loaf gently in a well-greased loaf pan (5x9-inch) and cover with plastic wrap. Repeat with the second loaf. Let double again in size, about 1 1/2 hours.
Preheat the oven to 350 degrees F. Once the dough has doubled (the loaf should be very puffy), place the two loaves on a shelf in the top half of the oven, well-spaced so that air can circulate between the loaves. Bake for thirty minutes or until done. The interior of the loaves should register at least 185 degrees F when an insta-read thermometer is inserted through the bottom crust. Remove the bread from the pans and cool on wire racks. Let it cool completely before cutting.