Beat cold cream until thick but not completely firm.
Pour the sweetened condensed milk into it and fold it in with a spatula or whisk.
Add lemon juice, zest, and vanilla and stir until smooth and even colored.
Pour into a large metal pan without a removable bottom (8-inch round or square pan or 2 medium loaf pans).
Drop teaspoons of the lemon curd on top of the ice cream. Lightly swirl using a smooth-bladed knife.
Freeze for 4-6 hours or until completely firm.
Scoop it into bowls and serve with sauces, fresh fruit, or plain.
Cover tightly with plastic wrap for longer storage, or use a freezer-safe container.