Makes 2 oval loaves
For sponge: Sprinkle dry yeast an sugar over warm milk (105 - 115 F) in small bowl; stir to dissolve. If using cake yeast, crumble into small bowl. Stir in sugar and lukewarm milk (95 F). Let stand until foamy.
Combine oats, bread flour and whole wheat flour in large bowl. Add yeast mixture and whisk until smooth. Cover with plastic wrap. Let rise in warm draft-free area for 1 hour.
For dough: Stir down sponge, using wooden spoon. Mix in 1 cup oats, butter and salt. Vigorously stir in enough whole wheat flour 1/2 cup at a time to form soft dough. Knead on floured surface until smooth and elastic, kneading in all-purpose flour if sticky. Grease large bowl. Add dough, turning to coat entire surface. Cover bowl with plastic. Let rise in warm draft-free area until doubled, about 45 minutes.
Gently knead dough in bowl until deflated. Cover and let rise again in warm draft-free area until doubled in volume, about 30 minutes.
Grease baking sheets. Gently turn dough out on lightly floured surface. Cut in half. Knead each piece into round. Pull 2 opposite sides under to form oval. Place on prepared sheets seam side down. Slash top of loaves, using serrated knife. Brush wit glaze and sprinkle wit oats. Let rise until doubled in volume, about 30 minutes.
Preheat oven to 400 F. Bake until loaves sound hollow when tapped on bottom, about 30 minutes. Immediately transfer to racks and cool.