Here's what you need:
2 lbs whole milk
8 oz granulated sugar
pinch of salt
1.25 oz cornstarch
1/3 oz cake flour
4 oz egg yolks
2 oz whole eggs
2 oz unsalted butter
vanilla extract to taste
Here's what you do:
First - make sure you have the following items -
a large heavy-bottomed stainless steel sauce pot
a wooden spoon
a wire whisk
two rubber spatulas
an ice water bath (a large metal bowl with equal parts ice and water - large enough for the sauce pot to fit into - and not so much ice water that it will overflow when the pot goes in.
Okay, now, here's what you do with everything:
Place 3/4 of the milk, about half of the sugar, and all of the salt, into the stainless steel pot.
Stir to distribute sugar and salt. Bring to a boil. Do not stir.
(Before the milk comes to a boil) Place flour and cornstarch in a bowl. Add remaining sugar
and milk. Whisk together to get rid of any lumps of cornstarch.
When smooth, add eggs and yolks, and whisk together.
When milk mixture has come to a boil, shut off the heat and - whisking constantly with one hand, ladle half the milk mixture a little at a time into the whisking egg mixture. This is called "tempering" - you're slowly bringing the eggs up to temperature, slowly so they don't become scrambled. Once about half of the milk has been whisked in, pour the mixture in the bowl back into the remaing milk in the pot - still whisking. Turn the heat back on and switch to the wooden spoon.
If you've used a rubber spatula to scrape any of this, toss that in the sink and use a clean one going forward.
Cook the mixture on medium heat, stirring CONSTANTLY. The mixture will be very liquidy at first,
but gradually it will thicken.
Once the mixture is pretty thick,
start tasting it. (Don't stop stirring).
Pay attention to the taste and mouth feel - if you taste or feel any chalkiness, keep stirring. The chalkiness is the uncooked flour.
Once there is no longer any chalky taste or texture, remove the pan from the flame (and shut the flame off), stir in the butter until melted completely.
At this point, place pot in the ice water bath and keep stirring.
When the mixture cools a bit more, stir in vanilla to taste.
Once the mixture has cooled, scrape it into a bowl or other container
and place plastic wrap directly on the surface of the pastry cream. This prevents a skin from forming.
Refrigerate until needed.