Mix all the ingredients for the Soaker thoroughly in a bowl. Add enough liquid to mix the dough. Cover with a lid or plastic wrap.
Mix all the ingredients for the Sponge thoroughly in a bowl. Add enough liquid to mix the dough. Cover with a lid or plastic wrap.
Place both bowls in a warm place for six hours or overnight.
Mix the contents of the Soaker bowl with the contents of the Sponge bowl until completely incorporated. I recommend using a mixer with the dough hook attached.
Add the ingredients from the Final Mix section until completely incorporated into the dough.
Remove from the mixing bowl and knead the dough for eight minutes. You may use a floured board to knead on to prevent the dough from sticking. Don't add too much flour or it will dry out the bread.
Shape the bread into a circle resembling a large donut or tire, with a hole in the center.
Transfer the dough to a cookie sheet lined with parchment paper. Cover with a light towel and allow to rise for an hour (or until doubled in size) in a warm place.
Using sharp kitchen scissors, make diagonal cuts along the edge of the round loaf. Turn the loaf as you make the cuts. Cut about three quarters of the way into the loaf.
Don't stress too much about measuring between cuts. This is a fun, festive bread that you shouldn't fret over!
Mix the egg with the water and brush lightly over the surface of the sun bread loaf. This step is optional, but it will give the finished bread a golden, sunny hue.
Bake 30-45 minutes at 350°F/176°C, or until an inserted thermometer reads at least 170°F/76°C. When you tap the bread, it should sound hollow.