The day, night, or at least 3 hours before, prepare the all butter crust.

Stir the flour, salt, and sugar together in a large bowl with a flat bottom. Add the butter pieces on top of the dry ingredients. Using your fingers, toss the butter in the dry mixture so each cube is coated. Use a pastry blender or your fingers to cut or rub the butter into the mixture until it is in pieces a bit larger than peas (a few larger pieces are okay; be careful not to over-blend). You want to be able to have big butter chunks in your crust: It helps create a flakey effect, as well as adding delicious buttery hits of flavor!

In a separate large measuring cup or small bowl, combine the water, cider vinegar, and ice.

Sprinkle 2 tablespoons of the ice water mixture over the flour mixture; do not add the ice, which is just there to keep your water cold. Using your hands in a circular motion, bring the mixture together until all the liquid is incorporated. Continue adding the ice water mixture, 1 to 2 tablespoons at a time.

Carefully mix until the dough comes together in a ball, with some dry bits remaining. Turn the dough out onto a lightly floured surface and knead gently until it comes into one mass; you don’t want to overwork it.

Separate the dough into two equal portions Shape each portion of dough into a flat disc, wrap in plastic, and refrigerate for at least 1 hour, preferably overnight before using.

Spray a 9-inch / 23cm pie plate (Stacey recommends aluminum steel ones for a better bake, ceramic plates are very thick) with non-stick cooking spray.

Take one piece of dough out of the fridge (leave the other in the fridge), and let it come to room temperature for about 5 minutes. Dust your work surface, rolling pin, and dough with flour, and roll out the dough so it’s about 2 inches (5cm) wider than your pie pan. Transfer the pastry to the pie plate. Press the dough into the pan, pushing it down into the bottom, sides and seams. Fold the overhanging dough under itself to form a neat, tight edge. (Also don’t worry if it isn’t neat, might was pretty jagged, so it will still be fine). Press the edge down so it’s sitting flat against the rim of the pie pan. Chill the pie crust in the fridge for 30 minutes.

Preheat oven to 220˚C / 425˚F.

Take the crust out of the fridge and prick it all over with a fork. Line the crust with 2 layers of foil and then fill with pie weights or dried beans, making sure the weights reach all the way up the sides of the pan. Place the pie pan onto a baking sheet. Bake for 20 minutes. Remove the pie weights and reduce heat to 190˚C / 375˚F and bake until a pale golden shade and the base looks partially cooked, about another 5 minutes. Allow to cool while you prepare the filling.

Heat a large pot or Dutch oven over medium high heat. Drizzle with 2 tablespoons of olive oil and add the onions, stirring until slightly softened, about 2 to 3 minutes. Add the garlic, tomato paste, mustard seeds and curry powder (if using) and stir until fragrant, 2 minutes. Add the potatoes and Jerusalem artichokes / sun chokes and stir to coat in the spices and then add the lentils, stock, and curry leaves, and season with about 1 teaspoon of salt and lots of black pepper. Bring to the boil and then cover, reduce heat to medium low, and cook until the lentils and vegetables are almost tender, about 20 to 25 minutes.

Meanwhile, whisk together 2 tablespoons of the flour with 1/4 cup water. Add the peas along with the flour slurry to the vegetables and stir constantly until the sauce is thickened. Taste and make sure you are happy with seasonings, adjusting salt and pepper if needed.

Take the second piece of dough out of the fridge and allow to come to room temperature for 5 minutes.

Preheat the oven to 200˚C / 400˚F. Scatter half the cheese onto the base of the cooled pie crust. Add the filling, as much as will fit, allowing it to dome in the centre. Take half of your remaining cheese and scatter on top of the curry filling.

Roll out the second piece of dough so that it’s about 1 to 2 inches wider than your pan. Place the dough on top of your pie and scrunch the edges in so that it is flush with the edge of the pastry case and then press it down to seal the edge. Using a tip of your knife or kitchen scissors, snip the pastry 3 or 4 times to allow steam to escape during cooking. Brush the top of the pastry with the egg wash and then top with the remaining cheese.

Place into the oven and bake for 15 minutes. Reduce heat to 180˚C / 350˚F and bake for another 15 minutes or until the top is golden and crispy.

Allow to cool for 10 minutes before cutting into wedges and serving. Eat with tomato sauce (ketchup), if you like, and a green salad.