Heat Milk: Place 4 cups whole milk in a medium pot and heat to 185-200°F (85-93°C), stirring frequently to preventing a skin from forming.
Cool Bath: Transfer the pot with milk to an ice bath (I filled my sink with ice and water), to cool milk to 100-110°F (37-43°C).
Mix: Add ¼ cup plain store-bought yogurt to the cooled milk and whisk well to combine.
Ferment: Cover jar or bowl with a lid, wrap in a moist, warm towel to keep in heat, and place in oven. Turn on oven light to keep warm, and let the bacteria do its yogurt making magic for 4 to 8 hours (or overnight).*
Strain: You can eat the yogurt like this, or strain it to make Greek yogurt. To strain, line a mesh sieve with cheesecloth (or paper towels, coffee filters etc), and pour yogurt in. Place over a large bowl and let strain in the fridge for a few hours (or overnight), until it’s reach a consistency you like.
Serve chilled with your favorite yogurt toppings, or use it in a recipe as you would store-bought yogurt!
