Dissolve citric acid in ¼ cup cool water. Pour into cold milk and stir gently. Heat milk to 90°F (32°C) over medium heat (do not boil).
Dissolve rennet in 2 tbsp cool water. Stir into milk using an up-and-down motion for 30 seconds. Cover and let sit 5–10 minutes until curds form (should look like soft gelatin).
Cut curds into a grid using a long knife. Heat gently to 105°F (40°C) while stirring slowly. Curds will shrink and separate from whey.
Scoop curds into a microwave-safe bowl or cheesecloth-lined strainer. Drain off excess whey.
Microwave curds 30 seconds, drain whey. Add salt. Microwave another 20–30 seconds, then stretch and fold like taffy until smooth and shiny.
Form into balls or logs. Place in ice water for 5 minutes to set shape.
Best eaten fresh (same day). Store in lightly salted water in the fridge up to 3 days.
