In the bowl of a stand mixer or a large mixing bowl combine 8 oz active sourdough starter, and 1/2 cup (2 1/2 oz) of the bread flour. Cover the bowl and allow the sponge to rise for 30-60 minutes.
Scald 8 oz whole milk in the microwave. Stir 1 ½ oz honey and 1 ½ teaspoons table salt into the milk then set it aside to cool to about 100°F (a little warmer than body temp). Add the cooled milk to the sponge in the mixing bowl. Add 5 oz old fashioned rolled oats. If using a stand mixer, switch to the dough hook.
With the mixer running, add the remaining bread flour. Knead the dough for 4-5 minutes until the dough gathers on the hook and clears the sides of the bowl. If mixing by hand, add as much of the flour by hand as you can then finish kneading in the remaining flour. Turn the dough out onto a lightly floured surface and knead into a smooth ball.
Place the dough into an oiled bowl, turning once to coat. Cover and set at room temperature for 1 hour. After an hour, with the dough still in the bowl use your hand to lift the top edge of the dough over into the middle of the dough. Repeat with the other 3 sides then flip the dough over. Cover and set at room temperature for another hour. Repeat the folding procedure 2 more times so the dough ferments for a total of 3 hours. By now the dough should be lively, elastic and airy. If the dough is still sluggish give it another hour or two at room temperature. After the initial fermentation the dough can be refrigerated for up to 2 days, or you can go ahead and shape and bake the loaf the same day.
Grease a 9"x 5" loaf pan with a light film of vegetable oil or cooking spray.
Turn the dough out onto a floured surface. Without kneading, pat the dough to a 9"x5" rectangle. Tightly roll the dough from the long side to form a log. Pinch the ends of the dough to seal.
Set the dough into the pan, seam side down. Cover with plastic wrap and set in a warm place and rise until the dough is almost doubled in size and fills the pan, about 1-1½ hours. If your dough is cold from the refrigerator the rising time may be longer. In the meantime, preheat the oven to 350 °F.
Use a sharp knife or razor to cut a ½" deep slash down the center of the loaf. Brush the dough with egg wash and sprinkle with rolled oats.
Bake about 40 minutes until golden brown and the interior temp is 200°F.
Cool in the pan for 5 minutes before turning out onto a cooling rack. Cool to room temperature before slicing.