The absence of any flour or custard powder means that the crème anglaise can’t be boiled or you will end up with scrambled milky eggs. To play safe, add 10 gr custard powder and boil the mixture for a minute to cook the custard powder. In that case, the eggs won’t scramble.
Test the thickness of the milk. The mixture is sufficiently cooked when it reaches 75°C and when you can draw a line on the back of a spoon.
At 75°C, they egg yolks are cooked enough to be safe to eat.
The amount of sugar is to taste.
Add flavours like chopped dark chocolate, instant coffee, chopped toffees, etc,