In the bowl of an electric mixer, weigh out the discard, water, yeast, honey and give it a quick mix with a spoon.
Weigh in both flours and salt. Using a dough hook, mix until shaggy (about 1 minute). Scrape the sides of the bowl if there is still loose flour.
Add in butter and knead 4 minutes on setting 3 or 4 of your mixer. It should form a ball and not be sticking the sides of the bowl. This can also be done by hand, but you'll want to make sure the butter is fully mixed in Cover with plastic and let rise until doubled, about 1 hour.
Butter, oil, or spray a long sandwich loaf pan* and set aside.
Once your dough has doubled, dump the dough onto a clean surface and flatten it with your hands. Roll the dough into a log and pinch the seam. Fold the ends under and pinch to seal. Roll the dough back and forth to seal the seams.
Place the dough into a long loaf pan, seam side down, spray/grease your plastic wrap and cover again to let rise until almost doubled, about 1 hour.
Preheat the oven to 400 degrees.
Take the plastic off, and bake for approximately 18-22 minutes until golden brown. Remove from oven but leave the bread in the pan for about 10 minutes. Optional: When the bread comes out of the oven, you can take a stick of butter and swipe it over the top. This gives a nice shine and makes the crust that much softer.
Gently ease the bread out of the pan and cool on a wire rack. Enjoy!