In a medium mixing bowl, combine condensed milk and hot water, mix until milk is completely dissolved. Add whole milk and culture, stir slowly until everything is combined. Strain the mixture through a fine mesh (if you want your yogurt has more sour taste, put more amount of culture).
Fill cleaned glass jars with milk mixture ¾ way full. Close with lids tightly.
If you use aluminum or stainless steel pot, line it with one layer of heavy duty foil. Skip this step if you use cast iron type of pot. Put jars in the pot. Pour hot water in, make sure water level is as high as milk level in the jars. Do not fill water all the way up to the jar.
Cover the entire put with heavy duty foil before close with the pot’s lid. Put the whole pot in turned-off oven or any where warm in the house (like closet, laundry room …).
Proof yogurt for 8 hours. You can proof up to 12 hours if desire more sour taste.
After proofing period, store yogurt in refrigerator for up to 1 week. Enjoy!