Special equipment: a candy thermometer and 8-inch tart pan
For the toffee: Line a baking sheet with parchment paper, and grease the parchment with oil. In a pan, bring 1/2 cup water to the boil with the dark brown sugar. When the sugar is dissolved, remove the pan from the heat and add the cream of tartar, golden syrup and black treacle. Return the pan to the heat, and cook until it reaches 284 degrees F on a candy thermometer. (This will take a while, but be patient and don't leave it unattended; it can burn very easily!) Once it reaches 284 degrees F, pour the mixture straight into the lined baking sheet, and leave to cool.
For the pastry: Cream together the butter and sugar in an electric mixer. Add the egg yolk and then the sifted flour. Mix to combine, but do not overwork. Wrap in plastic wrap, and leave to rest in the fridge for 1 hour.
Roll out the pastry on a lightly floured work surface to about 1/4 inch thick. Line an 8-inch tart ring with the pastry, and gently push it into the base. Line the pastry with plastic wrap, and fill with baking beans or rice. (Note: Not every type of plastic wrap is suitable for using with all foods. Check the packaging to see what foods and temperatures it can be used with. If unsure, use foil or parchment paper instead.) Place in the fridge for an hour to rest again.
Preheat the oven to 300 degrees F. Bake the pastry for 35 minutes, then remove the baking beans and plastic and bake for 5 to 10 minutes more, or until cooked all the way through and a light golden-brown color. Remove from the oven, and set aside to cool.
For the filling: Place the butter, sugar and orange zest in a pan, and heat until the butter and sugar are melted. Add the Bramley apples and cinnamon stick, and cook until the apples are very soft and turning into a puree. Add the eating apples, and cook for 1 to 2 minutes more, then remove from the heat. Pour the mixture into a colander or sieve to remove any excess liquid. Discard the cinnamon stick, and leave the apples to cool.
For the crumble topping: Preheat the oven to 350 degrees F. Mix the flour, superfine sugar, ground almonds, sliced almonds and butter together with your hands, using your fingertips to rub the dry ingredients into the butter. Place this mixture on a baking sheet, and bake for approximately 20 minutes, or until golden brown and crumbly. Stir the crumble every five minutes so that it cooks evenly. Remove it from the oven, and leave to cool.
To assemble the pie: Spoon the apple mixture into the cooked pastry shell. Break the toffee into chunks, and place a few over the top of the apple mixture (you will not need all the toffee). Completely cover the apple mixture with the toasted crumble, and dot a few more pieces of toffee on top.
Bake the pie at 350 degrees F for 10 to 12 minutes, or until the filling is bubbling and the toffee has melted.
Serve with custard, creme fraiche, ice cream or clotted creamor all four!
Golden syrup and black treacle are sweet byproducts of the sugar refining process and are popular in British cooking. You can find them at some specialty food stores and online markets.