Heat the whole milk and heavy cream in a saucepan until steaming, about 3–5 minutes, with small bubbles appearing at the edges. Keep it on low so it doesn’t boil over (visual cue: steamy surface, not rolling boil).

In a bowl, whisk the egg yolks, granulated sugar, and cornstarch until pale and thick, 1–2 minutes. The mixture should look slightly lighter and creamy (visual cue: ribbon-like thickness).

Slowly whisk the steaming milk mixture into the egg yolk mixture to temper it, a little at a time. Go gradually so the yolks stay smooth (visual cue: no scrambled bits forming).

Return everything to the saucepan and cook over medium heat, stirring constantly for 6–8 minutes, until thickened to a pudding consistency. Visual cue: it coats the back of a spoon and holds a line when you run a finger through it.

Remove the saucepan from the heat and stir in the fresh lemon juice, lemon zest, vanilla extract, and salt until fully combined. The mixture should turn bright and fragrant (visual cue: smooth, evenly colored pale yellow).

Cool completely over an ice bath for 10–15 minutes, stirring occasionally so it chills evenly. Visual cue: the custard becomes cool to the touch and thickens slightly.

Refrigerate the custard at least 4 hours, until very cold. Visual cue: firmed texture and chilled, scoopable consistency.

Churn in an ice cream maker on the lowest setting until dense and smooth, about 20–25 minutes. Visual cue: a thick, spoonable gelato consistency with minimal airiness.

Serve immediately for soft-set gelato, or freeze 1–2 hours for a firmer texture. Visual cue: gelato firms up and scoops cleanly from the container.