Finely grate the lemon zest.

Juice the lemons to get 1/4 cup of freshly squeezed lemon juice.

In a large bowl, whisk together the lemon zest, lemon juice, sugar, and salt.

In a measuring cup, whisk together the heavy cream and whole milk.

Gradually pour the cream and milk mixture into the lemon and sugar mixture, whisking constantly.

Continue to whisk until the sugar dissolves completely (about 2 minutes).

Pour the mixture into an 8-inch square metal baking pan.

Cover the pan tightly with aluminum foil.

Freeze for 2 to 3 hours, until the mixture is solid around the edges and mushy in the middle.

Stir the mixture well.

Cover the pan again with foil.

Continue to freeze for about an hour more, until completely firm.

Scoop the ice cream into chilled bowls and serve immediately.