You will need: 2 cups water, 1 cup evaporated milk, 3 teaspoons strong black tea, 4 green cardamom pods, a small piece of ginger, sugar to taste. Saffron or a pinch of cinnamon if you like.
Crush the cardamom pods lightly, enough to split them. Grate or bruise the ginger. Doing this releases the oils; whole pods thrown into water contribute almost nothing.
Bring the water, cardamom and ginger to a boil and let them go for two or three minutes before the tea goes anywhere near it. This is the step that separates karak from tea with milk in it. The spices need water and time; once milk is in the pan, extraction slows right down.
Add the tea and boil hard for two minutes. It should look far too strong. It is supposed to.
Add the milk and the sugar and bring it back to a boil, then drop the heat and let it tick over for three or four minutes. Watch it, because evaporated milk climbs the pan without warning.
Strain into cups from a height. This is not showmanship: it aerates the tea and softens the texture.
The shortcut that ruins it is boiling everything together from the start. You end up with a pan of sweet milk that tastes vaguely of tea, and no amount of extra leaves fixes it.
On sugar: karak is properly sweet, and making it half-sweet does not make it a lighter version of itself, it makes it unbalanced. If you want less sugar, make it weaker rather than less sweet.