Bring to simmer in 4 quart pot. CAREFULLY slide pot to one side of burner so it simmers on one side only. This makes it easier to skim.
Every hour use a ladle and skim the pot. Rinse ladle between uses and put in bowl of water to hold. When reduction reaches 1/4th original amount ladle into saucepan and reduce to 1 1/2 cups. Strain with fine meshed sieve. Cool and refrigerate.
Fresh: arrange in single layer in a wide skillet. Pour over broth and port. Liquid should be half way up pan. Cover and bring to simmer over med heat then reduce heat to med low and simmer gently for 30 minutes. Remove lid and simmer until liquid becomes a thick glaze about 10 to 15 mins more. Move pan quickly back and forth to coat chestnuts. Add cream at this point. Simmer two minutes more. Again move pan to coat. Season. Keep warm in oven for up to 30 minutes.
Cook same way but skip 30 minute cooking while covered.