Vinegar-Set Queso Blanco Avocado Toast

Steps

1. Wash a large heavy pot, a slotted spoon, a colander and a thermometer well, then line the colander with a double layer of clean cheesecloth and set it over a bowl.
2. Pour the 2% milk into the pot and heat over medium, stirring often so it doesn't scorch, until steaming and about 190°F (88°C) on the thermometer.
3. Turn off the heat and gently stir in the cider vinegar. Within a minute the milk curdles: soft white curds gather together and separate from thin, yellow-green whey. If the whey still looks milky, hold the pot near 190°F (88°C) for a few minutes more.
4. Rest the pot off the heat for 10 minutes so the curds firm up.
5. Ladle the curds and whey into the lined colander and drain about 15 minutes, until the cheese holds together but is still soft.
6. Turn the cheese into a bowl and crumble in the lemon zest and half of the salt. You'll have about 250 g of cheese, about 60 g (1/4 cup) per serving. For a firmer cheese, wrap it and drain or press it in the refrigerator at 40°F (4°C) or below for up to 30 minutes more.
7. Toast the whole-wheat bread until golden and crisp.
8. In a small bowl, mash the avocado with the remaining half of the salt.
9. Spread the avocado over the toast, crumble the lemon cheese on top, then add the tomato slices, green onion and red pepper flakes. Serve 2 toasts per person.
10. Refrigerate leftover cheese promptly in a covered container and use within 3 days; do not age it.