Dissolve yeast in warm water in a large bowl. Stir in milk then flour gradually. Beat until smooth.
Cover with dishcloth and let stand in a warm draft-free spot until starter beings to ferment (about a full day) (Bubbles will appear on the surface.)
If no bubbles form within 24 hours, trash and start over.
If bubbles have formed, stir, cover tightly and let stand in a warm dry place for 2-3 days or until foamy.
Once the starter becomes foamy you may transfer to a lidded jar and store in the refrigerator. It's ready to use when you can see a line of watery liquid at the top.
To use: Stir. Add one cup of starter in the recipe keeping the rest in the jar. Feed the starter in the jar with 3/4 cup milk and 3/4 cup flour. Store covered until bubbles appear then refrigerate.
Use starter on a regular basis or at least once a week.