Make crust first. Preheat oven to 350 F. Mix the crumbs, sugar and butter. Press evenly into a buttered 9 inch deep dish pie plate reaching up to but not over the rim. Bake for 10 minutes at 350 and let cool completely.
Stir together 1/2 cup of the brown sugar and the cornstarch in a bowl. Stir in 1/4 cup of the milk and the egg yolks; set aside. Bring the remaining 2 3/4 cups milk and the remaining 1/4 cup brown sugar and the salt to a boil in a non-reactive saucepan over medium heat.
When milk is boiling, whisk about 1/4 cup of the hot milk into the egg yolk mixture in bowl. Repeat 2 or 3 times. This helps prevent the eggs from curdling. Scrape the egg mixture into the saucepan and bring to a boil, whisking constantly. Be sure to whisk around the edge of the pan. Boil and whisk for 2 minutes. Strain the custard into a clean bowl. Whisk in the vanilla and butter. Place a sheet of wax paper or plastic wrap directly on the surface to prevent a skin from forming. Cool for about an hour at room temperature, then chill for at least 2 hours.
Pour the cooled custard into the crust. Top with wax paper and chill for a few more hours – preferably overnight.
Make sweetened whipped cream and pipe around edges.