In a large mixing bowl, combine three cups of flour, yeast, sugar, salt, and pepper. Mix well.

Heat soy milk, water, and oil until warm, and add to flour mixture.

Add mustard, minced onion, and egg. Blend at low speed until moistened.

Gradually stir in enough remaining flour to make a firm dough. Continue kneading for five to seven minutes, until dough is smooth and elastic. Place in a greased bowl, turning to grease top, and cover. Let rise for 50 minutes, or until doubled.

Punch down dough and divide into three parts.  Divide each third into six pieces. Shape each piece into a smooth ball, tucking ends under.

Cover; let rise until doubled, about 20–30 minutes.

Halfway through rising time, preheat oven to 375 degrees Fahrenheit (190 degrees Celsius).

While rolls are rising, combine boiling water and three tablespoons minced onion for topping, and let stand.

Combine onion mixture with slightly beaten egg. Brush tops of rolls with the mixture, scooping up onion as you do so. Sprinkle with black sesame seeds.

Bake for 15–20 minutes until golden brown.