Pour the condensed milk, vanilla extract and cream into a large bowl or food mixer. Whisk using the balloon attachment or hand whisk until thick (the mixture should hold its shape when you lift the whisk).
Take a loaf tin/pie tin or similar freeze-able container and spoon two-thirds of the cream mixture into it in large blobs. Add half of the lemon curd in small dollops over the top. Use a cocktail stick to swirl the lemon curd into the ice cream slightly.
Spoon on the remaining ice cream mixture, then dollop on the remaining lemon curd. Swirl again with the cocktail stick.
Sprinkle on the crumbled shortbread and place the ice cream in the freezer for at least 3-4 hours. (cover with a lid or clingfilm if freezing for longer).
Take the ice cream out of the freezer about 15 minutes before you want to eat it (to allow it to soften).
Nutritional Information is per serving (based on getting 10 servings from the ingredients).