Dump 2 1/4 cups milk, 4 egg yolks, 2/3 cup sugar, 1/4 cup cornstarch and 1/8 teaspoon salt into blender or food processor. (See notes if you need to do this by hand.)
Blend for about 10 seconds. There may be a lot of foam. That’s OK–it will disappear when cooked.
Pour into a 2-quart glass batter bowl. (DO NOT USE A SMALLER CONTAINER–it could boil over and make a mess.)
Cook in a microwave on HIGH for 5-7 minutes. Whisk well after 3 minutes and every minute thereafter. Microwaves vary wildly. If the pudding mixture is not thick after 7 minutes, keep cooking and stirring until the custard looks like pudding. It should heavily coat a spoon.
Stir 1 teaspoon vanilla bean paste or vanilla extract and 2 tablespoons butter into the thickened custard.
Press plastic wrap over the surface to prevent a skin from forming. Let cool on the counter (or in an ice bath if you are short on time) until lukewarm, then pour filling into prepared crust. Again press plastic wrap against the surface and refrigerate until filling is cold and firm.
Notes
Variation:Banana Cream Pie:Whisk cream filling and pour a thin layer into the pie shell. Slice and add a single layer of bananas, then cover with another layer of cream. Repeat. In the end, you should have three layers of cream with two layers of bananas, ending with the cream on top. Cover with plastic wrap pressed down to the surface of the filling.No blender or food processor?Use a whisk and some arm power instead of a blender. If you end up with any lumps, force the pudding through a strainer. It will be as smooth as silk