Preparation

Make the curds

• Dissolve the citric acid in ½ cup cool spring water. Pour the milk into a heavy stainless steel pot and let stand 15 minutes. Add the citric acid solution while stirring. over medium heat, warm the milk to 88°F to 90°F, stirring frequently.
• Just before using, crush the rennet tablet and dissolve in 1/4 cup cool spring water. Remove the milk from the heat, add the rennet solution, and stir lightly twice. Let the milk sit for 12 minutes. At this time, the curd (solids) should be pulling away from the whey (liquids). The curd will resemble silken tofu. With a long sharp knife, cut it into 1-inch cubes without removing it from the pot.
• Return the pot to medium-low heat and continually stir the curd until the temperature reaches 105°F, about 5 minutes.
• Place a colander in the sink, and spoon the cooked curds into the colander. (If you want to save the whey, strain the curds over large bowl.) Strain the curds well.

Make the stracciatella filling

• Remove one-quarter of the curds to a small bowl. Add the cream and 1/2 tsp. salt, combining the mixture with your fingers. Set aside. Transfer the remaining curds to a large bowl.

Make the burrata

• Heat a large pot of water (tap water is fine) until it registers 175°F to 180°F on a digital thermometer. Fill a large bowl with ice water and set aside.
• Work 2 Tbs. of kosher salt into the curds using your fingers. It will seem like a lot of salt, but don’t worry; most of it will remain in the water. Ladle or pour the hot water carefully into the bowl of curds—not directly onto the curds, but around them—until they are submerged. Let sit for 1 to 1-1/2 minutes.
• Stir the stracciatella filling and add more cream if it appears too dry.
• With your hands, gloved or bare (remember, the water is very hot!), gather half of the curds into a ball, lift it from the bowl and let it stretch back into the water. Continue to stretch it until it is shiny and elastic. The curds should immediately and effortlessly stretch. If they don’t, return them to the hot water until they are soft and pliable, and stretch easily. (Tip: if the water has cooled too much, drain it and add more hot water from the pot.)
• Working quickly, gently form the stretched mozzarella into a disk 5 to 6 inches in diameter and about 1/4 inch thick. Place the disk in the palm of your hand. carefully spoon 2 to 3 Tbs. of the stracciatella filling into the center of the mozzarella disk, adding 2 to 3 Tbs. more cream from the bowl. Twist the ball to seal. Place the burrata ball into the ice bath and let it cool until firm, 5 to 6 minutes. Repeat the process with the remaining curds, stretching and filling with the remaining stracciatella filling.
• Serve the burrata immediately, or enclose it in plastic wrap and refrigerate until ready to use. Serve within 48 hours.