1 quart plain whole-fat yogurt (not Greek yogurt, which is already drained)
1 cup + 3 Tbsp whey
½ cup sugar
Pinch of salt
Ground cardamom, cinnamon or grated lemon zest for garnish (optional)
Place the yogurt in a fine-meshed strainer or colander lined with cheesecloth. Place the strainer over a bowl and drain for at least 3 hours, or overnight.
Reserve all of the whey liquid. There should be about 2 cups of firm, drained yogurt. If necessary, return enough whey to the yogurt to make 2 cups.
In a medium saucepan, place sugar, salt and 1 cup whey. Bring to a boil, reduce heat to medium and cook, stirring frequently; adjust heat as needed so mixture does not boil over.
Cook until liquid boils off and the remaining syrup becomes deep brown, 20 to 30 minutes. Remove from heat.
Add 2 tablespoons of whey to pot and stir to blend well. If the mixture is too thick to stir, add another tablespoon of whey.
Allow the caramel to cool slightly, stirring frequently to make sure it remains fluid. (If the caramel stiffens too much to stir, place it over a pot of hot water and stir until fluid again.)
Add 1/4 cup of yogurt to the pot and stir vigorously to blend. Add the remaining 1 ¾ cup yogurt and stir to fully blend.
Transfer to a covered container and refrigerate until chilled, at least 30 minutes. If desired, serve garnished with a sprinkling of cardamom, cinnamon or grated lemon zest.