Combine two thirds of the flour with the sugar and salt in the bowl of a food processor. Pulse to incorporate. Spread the butter chunks evenly over the surface. Pulse until no dry flour remains and the dough just begins to form clumps. Use a rubber spatula to spread the dough evenly around the bowl of the food processor. Sprinkle with the remaining flour and pulse until the dough is just barely broken up.
Transfer the dough to a large bowl. Sprinkle the dough with water; then fold and press it until it comes together into a ball. Form into a 4-inch disk, wrap in clingfilm and refrigerate for at least 2 hours.
On a well-floured work surface, using a rolling pin dusted with flour, roll out the chilled dough into a 12 inch round. Transfer the dough to a pie pan. Press the dough evenly into the pan and use your prefered crimping technique to decorate the edges of the crust. Place the pan in the freezer for 2 hours before baking.
Pre-heat the oven to 190°C (170°C fan). Remove the pie crust from the freezer and line the inside with greaseproof paper. Place baking beans on top of the greaseproof paper to weigh down the crust. Bake for 15 minutes. Remove from the oven and remove the paper and weights. Return to the oven and bake for 10 minutes more, or until the crust starts to turn golden brown. Remove from the oven and leave to cool.
Turn the oven down to 180°C (160°C fan). Whisk together the eggs, melted butter, flour, sugar, brown sugar, cinnamon and vanilla extract until smooth. Stir in the chocolate chips, pecans and walnuts. Spread the mixture into the prepared pie crust.
Bake for 35 minutes, or until the filling is set and the top and crust are golden brown. Leave to cool and then serve.