The recipe calls for 4 Tablespoons Sour Dough Starter, I have always used at least 1/2 cup and sometimes as much as one cup. Anything over 1/2 cup, you will need to cut the milk and flour or it will rise way out of the pan.
SOUR DOUGH STARTER (Hitachi's Recipes)
2 Cups warm water or warm potato water and 2 cups flour.
2 Cups warm milk and 2 cups flour. flour.
1 pk yeast 2 cups warm water or milk and 2 cups flour I use #3. Put flour in crock, plastic ware or jar in a warm (not hot) place. Add water, milk or potato water. Let set for about 4 or 5 days until bubbly, then use in recipes.