In a large bowl, whisk the sweetened condensed milk, the lemon juice, lemon zest, vanilla and salt until combined.
It might take a minute or two for the lemon juice to fully incorporate with the sweetened condensed milk.
Using the spatula, pour ⅓ of the ice cream into a 9 x 5 loaf pan. Then drizzle 3 tablespoons of cooled lemon curd all over the top of the ice cream. Take a butter knife and make swirls.
Repeat this process for a total of 3 times.