Combine the yeast, sugar, and warm water together in a liquid measuring cup. Let sit 5 minutes.
Pour yeast mixture into the mixing bowl of a stand mixer (use the paddle attachment). Add buttermilk, oil, honey, and egg. Mix just long enough to combine.
Add whole wheat flour, salt, and baking powder. Beat at medium speed for 2 to 3 minutes.
With mixer on medium-low, gradually add the bread flour.
Turn dough out onto a lightly floured surface. I like to tape a piece of parchment paper to my counter for easy clean-up.Knead dough for 8 to 10 minutes.
Place dough in a well-greased large bowl, turnng to coat it. Cover and let rise until doubled in bulk, about 1 1/2 hours.
Punch dough down and divide in half. Roll each piece out into a 15x8-inch rectangle. Starting at the narrow end, roll it up. Pinch the ends to seal and tuck them under.
Place each loaf in a greased 8 1/2-by-4 1/2-inch loaf pan. Cover and let rise until doubled, about 1 hour.
Bake at 350 degrees for 30 minutes, or until sounds hollow when tapped. If bread is getting too browned, loosely cover with aluminum foil for the last 10 minutes of baking.Remove loaves from pans and let cool.