After 2-3 days of growth, cold crash the starter by placing in the refrigerator overnight. This will drop the yeast out of suspension and leave you with clear wort atop a thick cake of yeast. Just before you begin brewing, remove the starter gently from the refrigerator and place on the counter. When your boiling wort has cooled to the appropriate temperature, and it is well-aerated, gently decant and discard about 90% of the clear wort in your sink, being careful to leave some behind for swirling to make a slurry with the yeast cake on the bottom. Pitch that slurry into your aerated wort.