My Sitto and my mother and many other a Lebanese cook rinse the pan out with cool water before pouring the milk in, to help prevent burning the milk. I do not know if this practice is effective, but it is not mine to question. Read additional tips on making yogurt here.
Heat the milk: Rinse a large heavy saucepan (3-quart or larger) with cool water. Add the milk, and if using, clip a digital thermometer in the pan. Bring to just below a boil (210 degrees) at medium low heat, about 15 minutes. Stay nearby, because the milk will froth up and as it begins to boil it will rise up swiftly in the pan. Remove from the heat immediately.
Cool the milk and add the starter: Let the milk cool down to 110-115 degrees, stirring occasionally. If you are not using a thermometer, the equivalent is when your pinkie can just withstand being swirled in the milk for ten seconds. Arriving at this temperature can take an hour. If the milk cools below 110 degrees, gently warm it up to 110-115 degrees. If in this process of reheating, the temperature goes above 115 degrees, wait again until it comes back down to 110-115. Spoon a few tablespoons of the milk at this temperature into the yogurt (rawbi) starter, then stir that starter yogurt into the milk. You will notice a skin forms on the surface of the milk; that can be stirred right in with the starter, or spooned out.
Rest the milk: Remove the thermometer if you've used one, and cover the pan. Set the pan aside, undisturbed, in a warm spot for anywhere from 6 to 10 hours, or overnight. An ideal incubator is the oven, turned off (the oven can be heated on the lowest setting for a minute before placing the pan in, just to encourage warmth, but be sure to turn it off immediately).
Chill the yogurt: Remove the pot from the oven. The milk will have thickened into yogurt. Place, undisturbed as of yet, into the refrigerator for 1-3 days to further set the yogurt before eating or straining to thicken.
Congratulations: small batch, handcrafted deliciousness is yours. Check this out for more on straining the laban, and the very many special ways to enjoy eating it.