Place toasted walnuts in a food processor and process for about 30 seconds until they are ground into small pieces but not powder. Remove 2 tablespoons for garnish.

Add flour and salt and pulse to combine. Add cold butter and pulse until crumbly. Add ice water and process until it comes together in large clumps. Spray a 9 inch pie dish with cooking spray. Add the crust and press it onto the bottom and up the sides of the pie dish. Prick the bottom and sides with a fork and refrigerate for 15 minutes.

Preheat the oven to 350º. Place parchment paper over the crust and add pie weights or dried beans. Bake for 20 minutes. Carefully remove the pie weights and parchment paper and bake an additional 10 minutes until it is slightly browned. Cool completely.

In a medium saucepan, whisk the sugar, flour, and salt together. Slowly whisk in milk. Place over medium heat and cook, whisking constantly until thick and bubbly, about 3-5 minutes. Reduce to low and continue to cook for 2 minutes. Remove the pan from the heat.

Separate the eggs. Place the yolks in a measuring cup or glass bowl and beat with a fork. Add about a half of a cup of the hot milk mixture a tablespoon at a time to the egg yolks until the mixture is warm. Then slowly add the egg mixture to the milk mixture in the saucepan, whisking until incorporated, Return to low heat and cook for another 2 minutes until it is creamy and smooth. Remove from the heat and add butter and 2 teaspoons of vanilla. Place in a glass bowl and cover the top with plastic wrap pressing it to the surface. Let it cool for about 30 minutes, it should still be a little warm.

Slice bananas and place evenly over the bottom of the cooled crust. Pour the filling over the top and refrigerate for 3-4 hours until set. Top with whipped cream and serve.