In a small pot, add the milk and the granulated sugar and while stirring, heat until it reaches the temperature of your skin and lightly melt the sugar.
Separate the mixture from Step 2 into 3 batches and add to the bowl with the egg yolk in Step 1 and mix. If the temperature is too high, the egg will harden, so be careful!
In a different Teflon pot, add the flour and cornstarch and while stirring with a wooden spatula, heat on low for 1 minute to boil out the air. Don't burn it!! (You don't need to sift it!)
Add 1/3 of the mixture from Step 3 into Step 4. Mix with a whisk and raise the heat to medium. When it's mixed together, add the rest of the Step 3 mixture and mix together.
Boil the mixture until just before it becomes the consistency you want and turn off the heat.
While warm, add the butter and melt it. Strain through a colander. (Straining here makes smooth.)
Tightly wrap and let it cool as is.
Once cooled, add some drops of vanilla extract until the aroma is quite fragrant, mix it in, and it's all set.
Please use this for tarts, cream puffs, etc.
Story Behind this Recipe
There's a creme puff shop that is famous for it's creme puffs and I really wanted to make it myself, so I decided to experiment. If you have vanilla beans, it's even better, but I successfully substituted with vanilla extract. Even so, it's still perfectly delicious. It's a custard that will absolutely have people saying how delicious it is.
There wasn't really any difference when the powdered ingredients were sifted, so it's okay to just add them as is. When you add the eggs, they cook quickly, but please don't panic and turn off the heat too quickly. Heat until 1 second before the consistency you want!