In a large bowl, stir together 3/4 cup water and yeast. Let stand for 5 minutes. Meanwhile, in a small saucepan, heat and stir milk, sugar, butter, salt, feta cheese, Asiago cheese, olives, spinach, and garlic just until warm (120 degrees F to 130 degrees F) and butter almost melts. Stir milk mixture into yeast mixture until combined. Stir in flour (dough will be sticky). Lightly coat a medium bowl with cooking spray; transfer dough to the greased bowl. Lightly coat a sheet of plastic wrap with cooking spray; cover bowl with the greased plastic wrap and chill overnight.
Using a dough scraper or spatula, carefully loosen dough from bowl and turn out onto a floured surface. Cover with the greased plastic wrap and let stand for 30 minutes.
Grease a baking sheet; sprinkle lightly with cornmeal. Gently shape dough into an 11-inch long loaf. Transfer to the prepared baking sheet, using dough scraper or spatula if necessary. Cover and let rise in a warm place until nearly double in size (about 1 hour).
Preheat oven to 400 degrees F. In a small bowl, whisk together egg and 2 teaspoons water; brush over loaf. Bake in the preheated oven about 30 minutes or until an instant-read thermometer inserted in loaf registers at least 200 degrees F. If necessary, cover with foil during the last 5 minutes of baking to prevent overbrowning. Remove from baking sheet; cool on a wire rack.