Paska Russian Mennonite Easter Bread

1 package or 1 T. yeast
3/4 c potato water
1/2 c or more mashed potato
2 c flour
2 1/2 c warm milk
7 or 8 eggs, separated
1 1/2 to 2 c sugar
1 t lemon juice
1/2 c margarine
1 t salt
1/2 t grated orange rind
bit of vanilla

Soften yeast in lukewarm potato water for 10 minutes. Add a bit of flour to make a soft sponge. In the meantime, warm milk, pour it over 2 cups flour. Beat until smooth. Cool slightly. Beat egg yolks with 1 cup sugar and add warm flour mixture. Add stiffly beaten egg whites. Add yeast mixture. Let rise till light (covered). Add softened margarine, salt, 1-cup sugar and mashed potato. Add enough flour to make a medium soft dough (should be a bit sticky). Knead 10 minutes. Cover and let rise to double its bulk. Put on greased cookie sheets (I make round, oval, and braided loaves) and let rise again. Bake at 325 degrees F until golden. Careful not to overbake.
Ice with white icing.