For the crumb crust: Butter a 9-inch pyrex pie pan. Set a rack at the middle level of the oven and preheat to 350 degrees.
Place nuts in bowl of food processor fitted with metal blade. Pulse 10 or 12 times at 1-second intervals to finely grind without reducing to a paste. Remove cover and scrape inside of work bowl with a spatula.
Add remaining ingredients except butter and pulse once or twice to combine.
Add butter and pulse 3 or 4 times, until mixture is evenly moistened and looks crumbly. Remove blade and turn mixture out into prepared pan.
Using your fingertips, distribute the crumb mixture evenly over the bottom and sides of the pan, gently pressing into place. Make sure that the crumb coating is even because thin spots will burn during baking.
Use the back of a spoon to smooth the surface of the crust and to make the rim of the crust straight and even.
Bake the crust for about 20 minutes, or until the surface of the crust is a deep golden brown. Watch carefully, because the high sugar content makes them burn easily. Cool on rack.
To make the filling: Combine 2 cups milk, sugar and salt in a nonreactive saucepan; whisk once to mix and bring to a boil over low heat. Place remaining 1/2 cup milk in a mixing bowl and whisk in cornstarch, then eggs. Return milk and sugar mixture to a boil over low heat then whisk about a third of it into the egg mixture. Return milk and sugar mixture to a boil once more and whisk in the egg mixture, whisking constantly until the filling thickens and comes to a boil. Allow to boil, whisking constantly, for about 30 seconds. Remove from heat, whisk in butter and vanilla; pour into a nonreactive bowl. Press plastic wrap against the surface of the filling and chill until it is approximately 75 degrees. Spread the cooled filling evenly in the cooled crust.
To finish the pie, whip the cream with the sugar and vanilla until it holds a firm peak. Use a hand mixer on medium speed or a heavy-duty mixer fitted with the whisk. Spread the cream over the filling, making sure it touches the edges of the crust all around.