01 - Pour whole milk into a saucepan and place over medium heat. Stir occasionally to prevent scorching. Heat until the milk reaches 180°F, monitoring with a thermometer.
02 - Remove the saucepan from heat and let the milk cool down to 110°F. This temperature is optimal for activating the live cultures.
03 - In a small bowl, whisk together 2 tablespoons of the cooled milk with the plain yogurt starter until completely smooth and incorporated.
04 - Pour the starter mixture back into the saucepan with the remaining cooled milk. Gently stir to distribute the culture evenly throughout the milk.
05 - Transfer the milk mixture to a clean container. Cover and wrap the container in a towel to maintain warmth, or place in a yogurt maker. Let culture undisturbed for 6 to 8 hours in a warm location until the yogurt has set.
06 - Line a strainer with cheesecloth and place over a bowl. Pour the set yogurt into the cheesecloth-lined strainer. Refrigerate for 1 to 2 hours, allowing the whey to drain away until the yogurt reaches the desired thick consistency.
07 - Transfer the thickened Greek yogurt to a clean airtight container. Refrigerate until ready to use. The yogurt will keep for up to 2 weeks refrigerated.