Preheat oven to 170C fan

In a medium bowl, combine flour, walnuts, both sugars and cinnamon.

Melt butter and add to mix. Stir until crumbly.

Reserve about 1/3 of the mixture.

Pat remaining mixture into the bottom of an ungreased 13x9-inch baking tin. (If making a pie, press into bottom and sides of 9-inch pie tin and use all of the crumb base.)

Chill whilst making pumpkin custard.

In a stand mixer fitted with a paddle, combine pumpkin puree, sweetened condensed milk, eggs, cinnamon, vanilla extract, pumpkin spice mix and salt; mix well.

Pour evenly over chilled crust.

Mix reserved crumb base with additional flour.

Sprinkle over pumpkin mixture.

Bake 30 to 35 minutes until the custard is set.

Cool 10 minutes. Serve warm or at room temperature.

Store leftovers in the refrigerator.