Preheat the oven to 200 degrees C/180 C fan assisted. Grease a 23cm round pie pan or tart tin.

Lightly flour the work surface and roll out your dough to a circle roughly 30cm in diameter. Gently fit into the prepared pan, folding the overhang under itself at the rim to form a nice high edge. For a neater finish, you can trim the edges once blind baked. Crimp or decorate as you like then pop the tart shell in the freezer for 10 minutes.

Remove your tart shell from the freezer and prick the pastry all over with a fork. Place on a baking sheet, line with foil then bake for 15 minutes, pressing down any swells in the pastry as they rise (you'll see the foil bulge). Remove the foil then bake for a further 10 minutes, by which time the crust should be opaque and dry in places. Remove from the oven, brush over a thin layer of egg white then return to the oven for one minute more. Remove from the oven and set to one side while you make the filling.

In a medium saucepan, melt the butter over a medium-low heat. Pull the pan off the heat and stir in the sugar with a wooden spoon or spatula. Briskly beat in the eggs and yolk, then the syrup, vanilla extract, vinegar and salt. Return to the stove and warm over a low heat until the mixture has loosened and is no longer gritty, about 5 minutes. Remove from the heat and stir in the walnuts and oats.

Brush a second coat of egg white onto the pastry, followed by a glittering sprinkle of sugar. Scatter the cherries across the crust then carefully pour over the filling. Bake until gelled, slightly springy at the centre and with only the faintest wobble; 55 - 60 minutes.

Transfer to a wire rack and cool for at least 3 hours. Serve at room temperature, rewarmed or chilled, with cream, vanilla ice cream or crème fraîche.

Will keep for 2 days, covered, in the fridge.