In the bowl of a stand mixer, combine whole wheat flour, bread flour, kosher salt, and instant yeast.
Whisk together milk, water, honey, and oil. Add to dry ingredients and mix using the pad attachment until a shaggy dough forms.
If mixing by hand, use a stiff wooden spoon to mix the wet and dry ingredients together until you have a shaggy dough.
Knead with a stand mixer using the dough hook on medium speed for 5 to 8 minutes, adding up to 2 tablespoons of bread flour if the dough continues to stick to the sides of the bowl. Continue until dough is elastic and springs back when pressed.
For hand kneading: Knead on a lightly floured surface for 8 to 10 minutes. Fold the dough over onto itself, use the heel of your hand, push the dough away from you in a rocking motion, while also turning it about 90 degrees. Add up to 2 tablespoons of additional bread flour if it sticks to the surface or your hands.
Repeat this fold/push/turn process until the dough is smooth, elastic, and springs back quickly when you press it.
Shape dough into a ball, place in a greased bowl, cover, and let rise in a warm spot for 20 to 30 minutes or until doubled in size and it brings back slowly when poked with your finger.
Turn dough out onto a clean surface, shape into a loaf, and place in a greased 9x5 loaf pan. Cover loosely and let rise while preheating oven to 375°F, until dough is peeking over the edge of the pan.
Bake for 30 to 35 minutes, until an instant-read thermometer registers 190 to 205°F. Tent with foil if browning too quickly.
Cool in pan 10 minutes, then transfer to a wire rack to cool completely.