Stir together both flours, salt, powdered milk, and yeast in a 4-quart mixing bowl (or in the bowl of an electric mixer). Add the butter, honey, and water. Stir (or mix on low speed with the paddle attachment) until the ingredients form a ball. If there is still flour in the bottom of the bowl, dribble in additional water.
Sprinkle the counter with flour and turn the dough out onto the counter. Knead the dough for a full 10 minutes (it's good for those arms!), until the dough forms a smooth, elastic ball. Add additional bread flour, a bit at a time, only if needed to prevent the dough from sticking firmly to the counter. (The dough should be slightly sticky, so resist adding additional flour if in doubt. Adding too much flour may make the final loaf tough, so err on the side of not enough flour rather than too much.) Transfer the dough to a lightly oiled bowl and allow it to rise, uncovered, until doubled in size, about 90 minutes (my kitchen is hot, so this took only about 60 minutes).
Lightly grease a loaf pan with oil. Turn the risen dough out on a lightly floured counter and press into a rectangle about 6x8 inches. Roll the dough up from the short side into a loaf. Pinch the final seam closed and tuck the dough into the prepared loaf pan. Allow to rise, uncovered, until the dough fills the pan and rises slightly over the top of the pan, about 60 minutes. (Again, in my hot kitchen this took only 45 minutes).
Preheat the oven to 350 degrees F about 15 minutes before the dough has finished rising. Using a knife, cut diagnoal slices across the loaf (this is optional, I do it purely for aesthetics). Bake the loaf on the middle rack of the oven for 30 minutes and then rotate the loaf 180 degrees. Bake for another 15-30 minutes until it is a deep golden brown on top and registers 190 degrees F. in the center. Turn the loaf immediately out onto a wire rack and allow it to cool for at least an hour before cutting it into slices and serving.