Combine the milk and the diluted lipase, if using. Heat the milk to 86°F/30°C.
Add the starter, stirring to combine. Cover and allow the milk to ripen for 1 hour.
Add the diluted rennet and gently stir with an up-and-down motion for several minutes. Cover and allow to set at 86°F/30°C for 1 hour.*
Cut the curd into 1/2-1-inch cubes and allow to set undisturbed for 10 minutes.
Gently stir the curds for 20 minutes.
Pour the curds into a colander lined with cheesecloth.
Tie the corners of the cheesecloth into a knot and hang the bag over the sink to drain for 4 hours or more.
Untie the bag and cut the curd into 1-inch slices, then cut the slices into 1-inch cubes.
Sprinkle the cubes with the 3 teaspoons of sea salt to taste and then place in a covered bowl to age for 4-5 days in the refrigerator. Omit this step if you will brine the feta.
For that strong feta flavor, make a brine solution by combining 1/3 cup of salt and the water. Place the cheese in the brine solution and store in refrigerator for up to 30 days.**
If the curds are not setting firmly enough for you to cut easily, next time add 1/8 tsp. calcium chloride diluted in 1/4 cup water to the milk before adding the starter.