Place milk in a large, heavy saucepan over medium heat. Heat, stirring often, until a thermometer inserted into the milk reads 180 degrees F (82 degrees C). Turn off heat and let milk cool, stirring often, to 115 degrees F (46 degrees C).
Pour about 1 cup of warm milk from the saucepan into a bowl and whisk in yogurt. Pour this mixture back into the saucepan and stir to combine. Ladle the liquid yogurt into clean glass jars and cover loosely with lids.
Place the jars in a warm spot in your kitchen, wrapped in a towel if your kitchen is breezy. Let incubate until yogurt thickens, 12 to 24 hours.
Countertop or oven option: Cover and place the saucepan of liquid yogurt in a warm spot in your kitchen or in a gas oven with just the pilot light on. The time it takes to incubate depends on your environment temperature, culture strength, and other factors.
Slow cooker or Instant Pot® option: To speed up the process, place jars of liquid yogurt in your slow cooker or Instant Pot® and fill it with warm water. Set the device to Warm and let the yogurt sit until set, around 4 to 6 hours. You can also incubate the jars in an insulated cooler surrounded by warm water.
To make Greek yogurt, place yogurt in a strainer lined with several layers of cheesecloth, over a bowl or in the sink. Let drip for 30 minutes to several hours, until it reaches the perfect consistency for your tastes.
Per Serving: 156 calories;8.4 g fat;
11.7 g carbohydrates;
8.4 g protein;
26 mg cholesterol;
105 mg sodium.