In a large bowl (or the bowl of a stand mixer), combine the warm milk, softened butter, brown sugar, and salt. Stir until the sugar and salt mostly dissolve.

Add the whole wheat flour, bread flour, and yeast. Mix with a wooden spoon or the dough hook until a shaggy dough forms.

By hand: Turn the dough out onto a lightly floured surface and knead for 8–12 minutes until it is smooth, elastic, and slightly tacky (not sticky).

Stand mixer: Knead on medium-low speed with the dough hook for 6–8 minutes until smooth and elastic.

Place the dough in a lightly greased bowl, turning it once to coat. Cover with a clean towel or plastic wrap. Let rise in a warm spot (around 75–80°F / 24–27°C) until doubled in size, about 60–90 minutes.

Gently punch down the dough to release air. Divide it in half. Working with one half at a time, pat into a rectangle roughly the length of your loaf pan, then roll it up tightly into a log. Pinch the seam closed and tuck the ends under. Place seam-side down in a greased loaf pan. Repeat with the second half.

Cover the pans loosely and let the dough rise until it crowns about 1 inch above the rims of the pans, roughly 30–60 minutes. (Don’t let it over-proof.)

Preheat the oven to 350°F (175–180°C). Bake the loaves for 30–40 minutes, until the tops are golden brown and the internal temperature reaches 190–200°F (88–93°C). If the tops brown too quickly, tent loosely with foil for the last 10–15 minutes.

Remove the pans from the oven. Let the bread sit in the pans for 5–10 minutes, then turn the loaves out onto a wire rack. Cool completely for at least 30–60 minutes before slicing.