Heat milk until 180F scraping the bottom often (that’s right before boiling- do not let boil).
Remove pot from burner and add brown sugar. Mix until completely dissolved.
Add pot to ice bath until milk reaches 120F. Alternatively: Let cool on it’s own a couple hours checking periodically until 120F.
Wisk in yogurt with probiotics and flavoring (optional).
Pour into pint or quart jars.
On instapot, Select yogurt setting or “sous vide” and adjust to 115F for 9 hours (or lock lid and just leave alone for 8-9 hours). Alternatively, cover with thick towels for 8-9 hours.
Refrigerate for a few hours or overnight before using.