Heat milk in a heavy bottomed saucepan until it simmers. Remove from heat and stir in Buttermilk. Pour into a glass container and cover overnight.

The next morning line the colander with cheesecloth and pour the lumpy buttermilk into it. Cover with the ends of the cloth and let drain in sink for about 2 hours. You can also press the whey out to expedite the process.

When all the whey has been removed, place into a glass container with a lid and store in the fridge up to 4 days.