Under cold running water, use a brush to scrub carrots and potatoes, leaving on skin. Adjusting the size of the batches to suit the power of your juicer, juice the carrot, onion and potatoes separately. Save the juices in separate glasses.
Put the potato and carrot pulp into a bowl and mix well with a fork. Mix in the whole wheat pastry flour. Mix in the onion juice and 80% of the carrot juice. (You may drink the rest of the carrot juice).
Mix in the salt, nutmeg, baking powder and egg white. Add only enough potato juice to produce a loose pancake-like batter.
Heat a large, lightly sprayed, nonstick pan. Use a 1/3 cup measure to add the batter to the pan and spread into 1/2-inch thick pancakes. (Add more batter if necessary.)
Lightly brown about 3 minutes per side until crisp on the outside. Serve with nonfat sour cream.