To make the shortbread base

Prepare a deep, 8 inch square baking tin or dish. You can just grease it but I think as the butter melts it tends to 'fry'the outside. Cut a square of greaseproof paper to fit the tin. To do this I unroll the parchment over the tin leaving a three inch overhang each side cut the sheet from the roll then snip a diamond shape from each corner making sure that you cut down 3 inches. Place the paper into your tin overlapping the corners to fit.

Pre heat oven to 160C gas mark 3

Put flour, cornflour and sugar into a mixing bowl add the butter in one big lump. Work the dry mixture into the butter (easiest I find is using a fork) as the dough comes together lightly knead into a ball with your fingertips. Next gently press the dough into the prepared tin or dish making sure to get it into the corners.

Prick all over with a fork and place of on middle shelf of oven for 20 minutes

Whilst the shortbread is cooking prepare the Apple filling

Place all ingredients into heavy based saucepan and bring to the boil. Turn heart down so that the mixture cooks gently without caramelising or turning into jam. Keep stirring and checking if more water is needed. If extra water is required add 1 tablespoon at a time - you don't want the mixture too wet or it will soak through the shortbread.

Apple filling is ready when the small chunks of apple are sufficiently softened. Beat the filling in the pan with a wooden spoon to crush any large chunks

Prepare crumble

Put flour into a bowl

Cut butter into small chunks, add to flour and rub the mixture using the thumb and 2 fingers of both hands until it resembles breadcrumbs.

Stir in the sugar

Ready to assemble

Remove cooked shortbread from oven - shortbread should look undercooked and pale so it's very difficult to ensure it is cooked through. 20 minutes is a general time it is unlikely to take less time but perhaps a couple of minutes more, it should not start to brown.

Spread the apple mixture over the shortbread then spoon the crumble over to cover the apple.

Put it back in the oven and cook for 35 minutes - crumble should just be turning brown.

Remove from oven and allow to cool in tin for at least 30 minutes until you use the paper to lift out your finished crumblies (if you've left an overhang of paper it is easy to lift out)

Wait until cold until before cutting into three equal sections then cutting each section into 5 slices.

Eat them cold, with cream or ice-cream, warm them through to eat with custard or simply enjoy them as a very indulgent cake slice.