Pourable Skim Yogurt with Ginger-Mango Swirl

Steps

1. Wash a heavy pot, whisk, spoon, thermometer and a 1.5-quart jar in hot soapy water, rinse, then sanitize by pouring boiling water over them; let air-dry.
2. Heat: pour the commercially pasteurized skim milk into the pot and heat over medium-low, stirring often, until it reaches 180°F (82°C), then hold it at 180–185°F (82–85°C) for 15 minutes, stirring gently so it does not scorch.
3. Cool: take the pot off the heat and cool the milk to 108–112°F (42–44°C), setting the pot in a sink of cold water and stirring, about 15 minutes; check with the thermometer.
4. Add starter: in a small bowl, whisk the plain yogurt with a ladleful of the warm milk until smooth, then stir this mixture back into the pot.
5. Incubate: pour the milk into the sanitized jar, cover, and keep at 108–112°F (42–44°C) for 6–8 hours, in an oven with only the light on or wrapped in towels in a cooler, until softly set and tangy; skim yogurt sets loose and pourable.
6. Refrigerate: chill the yogurt right away at 40°F (4°C) or below for at least 2 hours until cold.
7. While the yogurt chills, toast the sesame seeds in a dry pan over medium heat for 2–3 minutes until golden, then let cool.
8. Make the ginger-mango swirl: blend the mango with the ginger, maple syrup and lemon juice until smooth, then refrigerate until serving.
9. Whisk the cold yogurt until silky (yields about 1 kg, about 1 cup per serving), divide among 4 glasses, spoon a quarter of the ginger-mango swirl into each, swirl, and sprinkle a quarter of the toasted sesame seeds on top. Keep leftovers refrigerated and use within 7 days.