Line a colander with 4 layers of cheesecloth, draping the edges over the sides, set in a large bowl
Add milk and thyme to a large stock pot. Bring to just under a boil over medium-high heat, about 5 minutes, stirring often with a wooden spoon to prevent scorching.
Reduce heat to medium low, add lemon zest and juice, and gently stir until curds form. This can take from 30 seconds to 2 minutes. Do not over stir.
Pour the liquid and curds over the cheesecloth lined sieve. Gather corners of cheesecloth together and gently squeeze out liquid, tie the opposite corners of cloth together to make a sack, and hang it form a large kitchen spoon or chop stick, suspended over a deep bowl. Set aside at room temperature until excess liquid has thoroughly drained from cheese, about 1 ½ hours. Transfer sack to plate, untie sack and untie cheesecloth, and loosely drape corners over cheese. Place a large heavy pot on top of cheese, then set aside for 30 minutes to compress cheese. Keep the whey in a large jar with tight fitting lid. For a creamier ricotta skip the last step adding the curds to a container with a tight fitting lid and refrigerate until ready to use
