1. Combine active dry yeast and 0.9 cups (215ml) of warm water, around 100°F (38°C), in a large mixing bowl. Let it sit for 5 minutes to allow the yeast to activate.

2. Add 2 teaspoons of salt, 2.2 cups (280g) of all-purpose flour, and 0.9 cups (115g) of coarsely chopped walnuts to the bowl. Mix well until a shaggy dough forms.

3. Gradually add 3.1 cups (390g) of whole wheat flour to the dough, one cup at a time, until the dough becomes smooth and elastic. Be prepared to stop adding flour when the dough feels right.

4. Knead the dough for 10 minutes until it becomes smooth and elastic. Use a stand mixer with a dough hook attachment or knead by hand.

5. Place the dough in a greased bowl, cover it with plastic wrap, and let it rise in a warm, draft-free place for 1 hour, or until it has doubled in size.

6. Preheat your oven to 375°F (190°C). Punch down the dough and shape it into a round or oblong loaf. Place the loaf on a baking sheet lined with parchment paper.

7. Bake the bread for 40-45 minutes, or until it's golden brown and sounds hollow when tapped on the bottom.

8. Remove the bread from the oven and let it cool on a wire rack for at least 10 minutes before slicing and serving.