Set aside 1 cup (250 mL) all-purpose flour. In a large bowl, combine remaining all-purpose flour and whole wheat flour with walnuts, wheat germ, sugar, salt and yeast.
Heat water, yogurt and butter in a small saucepan on low until hot but not boiling. Add to flour mixture, stirring to combine. Add enough of the reserved flour to make a stiff dough. Turn out onto a lightly floured surface and knead until smooth and elastic, about 10 minutes.
Divide dough in half and roll each out to a 12x8-inch (30x20 cm) rectangle. Starting at the short end, roll up each rectangle and place in greased 9x5-inch (23x13 cm) loaf pans. Cover and set in a warm place to rise until doubled in volume, about 1 hour.
Bake at 400°F (200°C) for 25 to 30 minutes, or until nicely browned. Turn out onto wire racks to cool.
Makes 2 loaves.