Chocolate Filled Doughnuts

4 1/2 cups flour
2 pkgs. dry yeast
1 tsp. grated lemon rind
1 cup milk
1/2 cup sugar
2 tsp. salt
1/4 cup oil
2 eggs
3/4 cup semi-sweet chocolate pieces
fat for deep frying
sugar or cinnamon-sugar

Stir together 2 cups flour, yeast and lemon rind. Heat milk, sugar, salt and oil over low heat only until warm, stirring to blend. Add liquid ingredients to flour-yeast mixture and beat until smooth; blend in eggs. Add 1 cup flour and beat 150 strokes. Stir in more flour to make moderately stiff dough. Turn onto lightly floured surface and knead until smooth and satiny, about 8 to 10 minutes. Shape into ball and place in lightly greased bowl, turning to grease all sides and place in a warm place until doubled, about 1 1/2 hours. Punch down. Let rest 10 minutes. Divide dough into 36 equal pieces. Flatten and place 6 chocolate pieces in center of each; seal edges securely. Let rise, sealed-side down, in warm place until doubled, about 30 minutes. Deep fry doughnut balls in preheated 375 degree fat 6 minutes, or until golden brown. Drain; coat with sugar or cinnamon-sugar.