To make the sponge, stir together the flour, sugar, and yeast in a small bowl. Add the water and stir until all the ingredients are hydrated and make a smooth batter. Cover the bowl with plastic wrap and ferment at room temperature for 60 to 90 minutes, or until the sponge gets foamy and seems on the verge of collapse.
To make the dough, combine the sugar, salt, powdered milk, butter, and shortening in a 4-quart mixing bowl (or the bowl of an electric mixer). Cream together with a sturdy spoon (or the paddle attachment) until smooth, then mix in the eggs and the extracts. Knead by hand (or switch to the dough hook attachment) and mix in the sponge and the flour. Add the water, as needed, to make a very soft dough. The finished dough should be very supple and soft, easy to knead, and not wet or sticky. It will take 10 to 12 minutes with the electric mixer and close to 15 minutes by hand to achieve this consistency. (Dough with high amounts of fat and sugar usually take longer to knead because the gluten requires more time to set up.) The finished dough should pass the windowpane test (see NOTE below) and register 77 to 88 degrees F. Lightly oil a large bowl and transfer the dough to the bowl, rolling it around to coat it with oil. Cover the bowl with plastic wrap.
Ferment at room temperature for approximately 2 hours, or until the dough doubles in size.
Remove the dough from the bowl and divide it into two equal pieces. Form each of the pieces into a boule. Lightly oil two 9-inch pie pans and place 1 boule, seam side down, in each pan. Mist the dough with spray oil and loosely cover the pans with plastic wrap.
Proof at room temperature for 2 to 3 hours, or until the dough fills the pans fully, doubling in size and overlapping the edges slightly. (If you only want to bake one loaf, you may retard the second in the fridge for 1 day, although it will take 4 to 5 hours to proof after it comes out of the refrigerator.)
Very gently brush the loaves with egg wash. Preheat the oven to 350 degrees F with the oven rack on the middle shelf.
Bake the loaves for 50 to 60 minutes, or until they register 190 F in the center. After 30 minutes, check the loaves and rotate 180 degrees, if necessary, for even baking. Because of the high amount of sugar, the dough will brown very quickly, but don't be fooled into thinking it is done. It will get darker as the center gradually catches up with the outside, but it will not burn. The final color will be a rich mahogany brown.
Remove the bread from the pie pans and place on a rack to cool. The bread will soften as it cools, resulting in a very soft, squishy loaf. Allow the bread to cool for at least 90 minutes before slicing or serving.
Recipe courtesy of Peter Reinhart's THE BREAD BAKER'S APPRENTICE (10 Speed Press, 2002)