- In large saucepan, combine wheat berries and cold water to cover by 2 inches.
- Cover and let stand at least 6 hours or overnight.
- Drain wheat berries.
- In same saucepan, bring 4 cups fresh water to a boil.
- Add wheat berries and ¼ teaspoon salt and return to a boil.
- Reduce heat to low and simmer until tender, about 30 minutes.
- Drain, rinse under cold running water and drain well. Set aside.
- Meanwhile, in medium saucepan, bring 2 cups water to a boil.
- Add millet and ¼ teaspoon salt and return to a boil.
- Reduce heat to low, cover and simmer until tender, 25 to 30 minutes.
- Remove from heat and let stand, covered, 10 minutes.
- Place in large, shallow container, fluff with fork and spread out.
- Let stand until cool.
- While grains are cooking, if using walnuts, preheat oven to 350°F.
- Spread nuts on baking sheet and bake until toasted, about 10 minutes. Set aside.
- In small saucepan, bring 3 cups water to a boil.
- Add sweet potato and ¼ teaspoon salt and cook until potato is just tender, about 6 minutes.
- Drain, rinse under cold running water and drain well.
- In large bowl, combine wheat berries, millet, sweet potato, toasted walnuts, scallions, celery, cucumber and apple.
- Add Mustard-Dill Dressing and toss gently but thoroughly to blend.
- Season with pepper and remaining ½ teaspoon salt.
- Cover and refrigerate at least 1 hour.
- Bring to room temperature before serving.