Pour 3 c. milk into a heavy-bottom saucepan. Sprinkle the sugar over the top (DO NOT stir!) and cook over medium heat until it begins to boil.
3 c. milk, 1/2 - 3/4 c. sugar
Beat egg and add the 1 remaining cup of milk and salt. Whisk.
1 c. milk, 1 egg, beaten, 1/4 tsp. salt
When the milk comes to a boil it will begin to rise. While whisking, slowly pour the egg mixture into the milk. Add the graham cracker crumbs, and bring it back to a light boil, whisking constantly. Cook until it is slightly thickened.
1 c. graham cracker crumbs (about 6 whole crackers)
Remove from the heat and add the vanilla.
1 tsp. vanilla extract
Place a piece of plastic on top of the pudding to prevent skin from forming on the top. Set aside to cool.
Serve warm, or cold with whipped cream and lots of graham cracker crumbs, and maybe some banana slices.
extra graham cracker crumbs and whipped cream, for serving
Refrigerate for up to 5 days.