2 cups sourdough starter 1 cup lukewarm milk 1 1/2 cup flour 2 eggs 1/4 cup oil 1/4 cup sugar 1 teaspoon salt 1/2 teaspoon soda 1 1/2 cup flour, divided, plus extra as needed Combine the sourdough starter, milk, and 1 1/2 cups flour in a bowl and mix until smooth. Add the eggs and oil and beat well until completely combined. In a small bowl, mix together the sugar, salt, baking soda, and 1/2 cup flour. Mix well then work into the dough. Spread 1 cup of flour on a work surface. Place the dough on the flour and knead the dough until the dough is soft and most of the flour has been worked into it. Grease a bowl, place the dough in the bowl, cover with waxed paper and let rise in a warm, draft free place until doubled in size. Add the remaining 1/2 cup of flour on a work surface. Roll the dough out on the floured surface until it is 1/2-inch thick. Cut with donut cutters. Place the dough on a floured baking sheet and let rise, uncovered, until doubled in size. Heat oil to 365 degrees F in a deep fryer or deep, heavy skillet. When hot, add the donuts in batches and fry until golden brown. Remove from the oil and let drain on paper toweling. Store the donuts in an airtight container.