My mother's dal has a texture that mine did not have for a very long time. Thick without being stodgy, creamy without any cream, and it holds together on a spoon instead of running off it.
I assumed for years that she was using less water. She was not. The water was never the problem.
Undercooking is the main culprit
Most people, including me for a long time, stop cooking dal when the lentils are soft. Soft is not the finish line.
What you want is for the lentils to break down completely, to the point where they stop being distinguishable as individual pieces and start becoming a single mass. In toor dal that takes considerably longer than the point at which they become edible.
In a pressure cooker, the difference is maybe three or four extra whistles past the point where it is technically done. On an open pot, it can be another twenty minutes.
The test I use now is to press a lentil against the side of the pot with a spoon. If it squashes into a smear with no resistance, it is done. If it squashes into a soft lump that still holds a shape, it needs more.
The mashing step nobody mentions
After cooking, most Indian households whisk or mash the dal. This is not a decorative step and it is frequently left out of written recipes.
Mashing releases starch. That starch is what thickens the liquid and gives the finished dal its body. Dal that is cooked and then left alone stays as lentils sitting in water, regardless of how well cooked those lentils are.
A few vigorous passes with a whisk or the back of a ladle changes the texture completely. It takes about thirty seconds.
Old lentils behave differently
This one took me an embarrassingly long time to work out, and it explains why the same recipe sometimes works and sometimes does not.
Lentils that have been sitting in a cupboard for a year take substantially longer to cook and never quite break down the same way. They also absorb water differently, which is why a recipe that worked last month can produce something thin today.
There is no way to tell by looking. What you can do is buy from a shop with turnover, buy smaller quantities, and if a batch is taking unusually long, accept that and cook it longer rather than assuming your timing is wrong.
Soaking helps with old lentils more than with fresh ones, which is a reasonable diagnostic in itself.
The tempering is not just flavour
The tadka poured over at the end does something structural as well as aromatic.
The fat emulsifies into the starchy liquid, and that emulsion is part of what makes dal feel creamy rather than watery. Skimping on the ghee or oil produces a thinner mouthfeel even when everything else is right.
This is also why dal made with a proper amount of fat tastes richer than the calorie difference would suggest. It is not just the fat, it is what the fat does to the texture.
I use more than I used to and less than restaurants do, which is probably the right place to be.
Salt timing, which is genuinely debated
There is a persistent belief that salt added early prevents lentils from softening. I have tested this on my own stove enough times to have an opinion and not enough to be confident.
What I observe is that salt early does slow things down somewhat, noticeably with older lentils and barely at all with fresh ones. The effect is real and smaller than the folklore suggests.
My practice is to salt after the lentils have broken down, mostly because it is easier to judge the seasoning once the volume has settled. That is a practical reason rather than a chemical one.
Resting
Dal thickens as it sits, sometimes dramatically. Something that looks correct in the pot can be noticeably thicker twenty minutes later.
Which means judging the consistency at the moment of cooking is misleading. I now aim for something slightly looser than I want, and let it come to where it should be while everything else finishes.
The corollary is that leftover dal from yesterday is nearly always too thick and needs water and a brief reheat. That is normal and not a sign that something went wrong.
What I would tell someone starting
Cook it longer than you think. Mash it. Do not skimp on the tadka. And if it is still thin after all of that, your lentils are old.
The thing I wish someone had said to me is that the target is not "cooked". The target is "collapsed", and there is a substantial gap between the two that the recipes do not describe.
The pressure cooker complication
One thing that muddies all of this. Pressure cookers cook lentils fast enough that you can hit soft without going anywhere near collapsed, and the whistle count everyone quotes is calibrated for soft.
Three whistles gets you cooked. Six or seven gets you broken down, and the difference in the finished dal is obvious once you have tasted them side by side.
The other thing about pressure cooking is that almost no water evaporates, so you finish with as much liquid as you started with. Open cooking loses a good deal, which is part of why an open pot dal often looks thicker for the same starting quantities.
What I do now is pressure cook longer than seems necessary, then leave the lid off for the last five minutes with the tadka going, which lets some water off and lets me judge the final consistency properly.