Preheat the oven to 200C/400F/Gas 6
Mix together the flour, cornflour and salt. Using your fingertips rub in the lard and butter until the mixture has the texture of breadcrumbs.
Stir in the sugar then gradually add the milk until a soft dough is formed. You may not need to use all the milk.
Lightly knead the dough on a floured surface until a smooth dough is formed (this won’t take long).
Roll out the dough to a rectangle measuring 50x20cm/20x8in. Spread the jam over the dough.
Roll the dough from the longest side as if rolling a Swiss roll. Bring the ends together and stick them together using a little milk. Shape the ring into a heart shape.
Make small incisions over the surface of the heart shape. Brush the top with milk.
Bake for 15-20 minutes until golden-brown and the base is cooked through.