In a small bowl, combine the citric acid with ¼ cup (2 fl oz/60 ml) water and stir until combined. Set aside.

In another small bowl, combine the rennet with the remaining ¼ cup (2 fl oz/60 ml) water. Stir until combined, then set aside.

In a large pot over medium heat, combine the milk and citric acid mixture and stir for 30 seconds until completely mixed.

Using a thermometer, and stirring the milk frequently, heat to 90°F (32°C). This should take about 5 minutes.

Remove from the heat and stir in the rennet mixture for a full 30 seconds. Be sure to stir the milk from the bottom to the top so that it is completely and evenly mixed in.

Put a lid on the pot and don’t disturb it for 5 minutes.

Check to see if the curd has formed by slipping a knife between the milk and the side of the pot. If it comes away slightly, move on to the next step. If not, leave for another 5 minutes.

Using a large knife, cut the curd all the way to the bottom in roughly 1-inch (2½-cm) strips. Then cut in the opposite direction to make a grid pattern.

Return the pot to the stove and warm over low heat to 105°F (40°C) for about 5 minutes. Gently agitate the liquid without breaking up the curd to ensure even heating.

Once again, remove the pot from the heat and let it stand for 10 minutes.

While the curd is resting, place a fine-mesh sieve over a bowl and line the sieve with cheesecloth.

Using a slotted spoon, lift the curd out of the pot and place it on the cheesecloth to drain.

Firmly press on the curds to squeeze out as much whey as possible, using the cheesecloth to help squeeze.

Stir 3 teaspoons of salt into the liquid (whey) in the pot, then remove 4 cups (32 fl oz/260 ml) whey to a medium bowl. Heat the remaining whey to 175° F (80°C).

Place the curd into the hot whey for about 10 seconds. Remove with a slotted spoon, and then stretch and fold the curd a few times using gloves to protect your hands from the heat.

Return the curd to the whey for another 10 seconds, then remove, and this time, stretch the curd and sprinkle on the remaining teaspoon of salt. Fold and stretch a few times, then return to the whey when it cools down.

Continue this process 2 or 3 more times until the curds start to look like smooth, silky, shiny mozzarella.

When you are done, create a smooth ball, tucking the edges underneath. Place this mozzarella ball into the hot water to seal the shape, then place it in the reserved cool whey to let it set for 15 minutes. Serve or use immediately.