Crack your eggs into an appropriately-sized bowl for whisking. You'll need to whisk them really well. A fork works, also. How many eggs do you whisk up? Well, that depends upon your personal preference. The more eggs added, the firmer the final custard. I don't like really runny custard. It makes a fabulous base for ice cream, though. I also don't like super firm custards like most of the savory custards I've had before. I like mine somewhere in the middle, but I don't have an exact, preferred thickness. I like to go somewhere around 1/2 to 1 egg per cup of liquid, usually closer to a 1:1 ratio. Today I am using 6 eggs.
Whisk them really well. Like to within a few seconds of your wrist falling off from exhaustion well. Then add some of the milk and whisk them even more. You want to get as much of the whites mixed in as you possibly can. Unblended white bits floating around will leave unappetizing, possibly rubbery-textured bits in your finished custard.
When you have them all whisked up, either skim the foam and superfluous bits of egg whites out with a fork or slotted spoon, or do like me and pour them through a sieve. but before we get to that part! Make sure the sugar is all mixed up in your milk. Unmixed sugar will leave a gritty, super-sweet layer at the bottom of your otherwise awesome custard. Yuck. So go do some more mixing. Of both the eggs and the milk. And find your sieve if you have one.