An Indian gravy that coats the back of a spoon almost never contains a flour thickener. The body comes from solids already in the pot and from water leaving it.
Ground solids do most of the work
Cashews, melon seeds, poppy seeds, almonds and coconut are soaked and ground to a paste that suspends in the liquid. Their fat and starch hold the sauce together without gelling it.
A paste like this thickens by volume rather than by chemistry. The gravy stays pourable and glossy instead of turning to the thick, slightly gluey texture a flour-based sauce takes on.
That distinction matters for reheating. A nut-thickened gravy loosens with a spoon of water and returns to its old texture, where a starch-set sauce often turns pasty.
Pulses dissolve into the liquid
Many everyday gravies get their body from a handful of split lentils cooked until they collapse. The pulse gives up starch and protein and stops being a visible ingredient.
Cooks often use this deliberately in vegetable curries, adding a small quantity of split pigeon peas or split chickpeas that would be too little to notice as a component.
Because the thickening is protein-heavy, these gravies set noticeably as they cool. What looks thin in the pan will be considerably firmer in a storage container the next morning.
Reduction is a thickener in its own right
A long simmer removes water, concentrating everything left behind. This is the slowest route to body and the one that also does the most for flavor.
Indian home cooking usually reduces with the lid off after the aromatics are cooked down, which is why recipes call for the oil to separate and pool at the edges.
American stoves and wide pans favor this method. A broad skillet evaporates faster than a tall pot, so the same gravy tightens in less time on a US range.
Dairy behaves differently from the rest
Cream and reduced milk add richness and a small amount of body, but they thin a gravy before they thicken it, because they arrive as liquid.
Their real contribution is textural coating rather than structure. A splash of cream at the end softens the edges of the spices and makes the sauce cling to bread.
Dairy also has to be handled carefully once acid is in the pot, since tomato and yogurt together push a gravy toward the point where milk proteins separate.
Choosing the route changes the dish
Each thickener carries flavor as well as texture, so the choice is not neutral. Coconut sweetens, cashew rounds, lentils add earthiness, and reduction deepens what is already there.
This is why a recipe rarely lets you swap one for another. Substituting a nut paste for reduction gives you the right thickness and the wrong depth.
Cost pushes in the same direction. Nut pastes are the expensive route and reduction is the cheap one, which is part of why restaurant gravies and home gravies feel different.