In a large mixer bowl thoroughly combine 3 cups plain flour, sugar, salt and undissolved yeast.Combine milk, water and butter in sauce pan.
Heat over low heat until liquids are very warm, 120°-130°. Butter does not need to melt.
Gradually add to dry ingredients and beat 2 minutes at medium speed on mixer, scraping bowl occasionally.
Add remaining cup of plain flour and beat at high speed 2 minutes.
Stir in enough wheat flour to make a stiff dough.
Sprinkle board or cloth with whole wheat flour, turn out dough and knead until smooth and elastic, about 8 to 10 minutes.
Cover with plastic wrap, then a towel.
Let rest 20 minutes.
Divide dough in half.
Roll each half into a 14"x9" rectangle.
Roll up dough, press down ends and fold under.
Place in 2 well-greased loaf pans.
Brush loaves with oil, cover with plastic wrap.
Refrigerate 2 to 24 hours. When ready to bake, remove from refrigerator.
Uncover dough carefully. Let stand at room temperature 10 minutes.
Puncture any gas bubbles which may have formed near surface.
Bake at 400° for about 40 minutes, or until done.
Remove from pans and cool on wire rack.