Day 1 (Day 6): Remove 1 cup fed sourdough starter at 100% hydration. Add to a large glass storage jar (we use these) or mixing bowl. Add 1 cup flour, 1 cup sugar, 1 cup milk. Mix well and cover loosely. Store in a warm area of your kitchen. Since you already have a mature starter, you skip to the front of the line -- your Day 1 is considered Day 6 (refer to these original instructions if you're confused).
Day 7: Mix well.
Day 8: Mix well.
Day 9: Mix well.
Day 10: This is your first official baking day with your new starter. Congrats! Stir or mix the starter well. Feed 1½ cup each flour, sugar, milk. Mix well then divide into equal portions of 1-cup each (we use 1-gallon freezer bags for easy sharing and storage). Reserve one cup to bake with, one cup to leave on the counter, one cup to freeze for future or emergency use. Share or freeze the remaining starter.