Dissolve yeast in water. Add sourdough starter. Mix in 1 cup flour. Let mixture set 12 hours or overnight to develop sponge. Stir sponge to dissolve crust. Add sugar, 2 eggs, butter, and salt; mix well. Add 2 1/2 cups flour to sponge; mix well. Pour 1 cup flour on kneading surface. Pour sponge mixture on flour. Cover with 1 cup flour. Knead until flour is worked into dough. Continue adding flour until stiff dough has formed. Knead dough 10 minutes or until folds form. Place in greased bowl. Grease top. Cover; let rise until doubled in size. Punch down dough. Knead 2 minutes. Divide dough into 2 equal balls; divide 1 ball into 8 equal parts. Roll 8 parts until approx. 12 inches long. Place these 8 strips side by side; braid by folding 1 strip over the other in numerical order. Tuck in edges. Prepare second dough ball in same manner. Place braids on greased cookie sheets. Cover; let rise until double in bulk. Brush braids with 2 eggs. Bake in preheated 350F oven 30 minutes or until golden brown. Remove from oven; brush with oil. Cool on rack. Yield: 2 loaves.