Grease a 22-24cm loose-bottomed flan tin with butter.

Preheat the oven to 200C / 180C Fan / Gas 6.

Make the base:

Stir together the flours, oatmeal and salt.

Rub in the butter so the mixture resembles breadcrumbs.

Stir in the sugar.

Press the mixture evenly into the base of the flan tin, smoothing over with the back of spoon.

Peel the apples, cut them into quarters and cut out the cores.

Taking a quarter at a time, slice the apple thinly but hold them together.

Lightly press down so that the slices fan out.

Still keeping the slices together, transfer to the flan tin, placing either at at an outer edge or in the middle to start making concentric circles of apples.

Repeat with each quarter of apple: slicing thinly and transferring to the base. Place them closely together so that all the apples fit on and no base is showing.

Mix together the Demerara sugar and the cinnamon.

Melt the butter and brush it all over the apples.

Sprinkle with the sugar-cinnamon mixture.

Place the tart in the oven and cook until the apples are soft and caramelized on top (35-40 min).

Place on a wire rack until completely cold before running a knife around the edge of the tart and removing from the tin.

Serve at room temperature either on its own or with pouring cream.