https://www.seriouseats.com/2018/08/how-to-make-fior-di-latte-gelato.html
In Italian, fior di latte is a figure of speech (flower of milk) indicating something made with cow's milk of the highest caliber, like mozzerella. In this case, it refers to gelato in its purest form: no eggs, no fruit, no chocolate, or even vanilla—just pure dairy. For that reason, it's vital to use the freshest, most flavorful milk and cream, from grass-fed cows. It's a perfect excuse to splurge on a few bottles from a local dairy, but if that's not an option there are a few national brands that are more than adequate to the task (see note).
Milk from grass-fed cows has a bolder dairy flavor, giving the gelato more character.
Holding the gelato base at a boil for 60 seconds ensures that the cornstarch is fully dissolved, eliminating any trace of starchy taste or texture.
Reserving some of the milk and cream off-heat preserves their fresh flavor, while helping the base to cool faster.
Ingredients
9 1/4 ounces plain or very lightly toasted sugar (about 1 1/3 cups; 265g)
1 1/4 ounces cornstarch (about 1/4 cup; 35g)
1/2 plus 1/8 teaspoon (2.5g) Diamond Crystal kosher salt, or more to taste; for table salt, use about half as much by volume or the same weight
20 ounces best quality whole milk, preferably grass-fed, divided (about 2 1/2 cups; 565g)
8 ounces best quality heavy cream, preferably grass-fed (about 1 cup; 225g)
Directions
Whisk sugar, cornstarch, and salt together in a 3-quart saucier. When no lumps of cornstarch remain, add exactly 14 ounces of the milk (about 1 2/3 cup; 396g) and whisk to combine. Cook over medium heat, whisking constantly but not vigorously, until it begins to simmer. This will take about 6 minutes, if the process seems to be moving slowly, simply turn up the heat. When the mixture comes to a boil, set a timer and continue cooking and whisking for exactly 1 minute. This ensures the cornstarch is fully hydrated.
Immediately transfer mixture to a large bowl, then whisk in the remaining milk and cream. Bearing in mind that the gelato will taste substantially less sweet once frozen, season with an additional pinch of salt, if desired. Cover and refrigerate the gelato base until cold, thick, and no warmer than 40°F, about 3 hours (this process can be sped along with an ice bath if time is of the essence; in that case, a stainless steel bowl will help cool the base even faster).
Churn in an ice cream maker according to the manufacturer’s directions. Meanwhile, place a quart-sized container and flexible spatula in the freezer. When gelato looks fluffy and thick, shut off the machine and, using the chilled spatula, scrape gelato into the chilled container. Cover with plastic wrap pressed directly against the surface of the gelato, and freeze until thick enough to scoop, about 4 hours.
Gelato is typically served at about 16°F, while most American freezers run at 0°F; for the most authentic presentation, soften gelato to 16°F in the refrigerator before serving. In a squat container, like a yogurt tub or a square storage container, this will take about 45 minutes. The timing will vary substantially depending on the size, shape, and material of the container (such as a metal loaf pan or glass baking dish), so check on the gelato frequently to ensure it does not melt.
whisk in exactly 14 ounces of milk. It may seem like the gelato could be made faster by heating less milk, but in a sugar-based solution, the cornstarch won’t fully dissolve in a smaller volume of milk—the result would be a thinner bodied base with a very starchy taste and texture, and an icier finished product. Also, since the cooking process will very lightly “toast” the lactose, coaxing out some faint toffee notes (more on that in a bit), adding less dairy at this stage will result in weaker flavor.