
In a large bowl, combine sourdough starter, 1 cup of warm water and 1 cup of flour. Cover and let stand overnight. Sprinkle yeast over 1/4 cup of warm water. Set aside to soften 5 minute. Stir softened yeast mixture into overnight sourdough mixture. Stir in salt, oil and sour cream mix. Stir in enough flour to form a soft dough. Turn out onto a lightly floured surface. Knead dough 8 to 10 minutes or until smooth and elastic. Cut dough in half to make two loaves. Cover with plastic wrap and let rise 50 to 60 minutes or until doubled in size. In a small bowl, beat egg. Beat in 1 tablespoon water. Brush egg mixture over surface of loaf several times as dough rises. Preheat oven to 350F . Bake loaf 40 minutes or until golden brown. After 30 minutes, if loaf is golden brown, cover with a tent of foil to prevent further browning. Remove from baking sheet, place on wire rack to cool.