Place milk in a large saucepan and heat until the milk begins bubbling around the edges and climbing the sides.
Remove from heat and cool to 95 degrees F
Once cooled, pour through a fine meshed sieve and discard any solids.
In a separate bowl, mix some of the cooled and strained milk with the yogurt until blended and smooth, then blend back in with the rest of the milk.
Pour into a glass container that will fit in your crockpot
Line the crockpot with an old towel, and place your glass container inside the crock. Cover the crockpot (not the glass container)
Use the "warm" setting for 8-10 hours (you don't want it to go above 115 degrees)
Pour off the whey, and blend the yogurt til smooth (not everyone does this - I like my yogurt thick, though - you might like to pour off just some of the whey)