The perception that Indian cooking is slow comes from a specific stage, not from the whole process. Once that stage is separated out and made in advance, weeknight cooking looks completely different.
Where the time actually goes
Peeling and chopping onions, grinding ginger and garlic, then browning the onion properly accounts for most of the elapsed time in a typical gravy.
The remaining steps, adding spice, liquid and the main ingredient, take a fraction of that and cannot be shortened much anyway.
Moving the first stage out of the weekday evening therefore removes the majority of the effort rather than a portion of it.
Why the paste keeps well
A cooked aromatic paste has had most of its water driven off and is held under a layer of fat, both of which slow spoilage considerably.
The fat also excludes air from the surface, which limits oxidation of the aromatic compounds that would otherwise fade first.
Refrigerated in a sealed jar it holds for a week or more, and frozen in portions it holds far longer with little change.
Portioning is what makes it usable
A single large container defeats the purpose, since it has to be thawed whole and refrozen. Freezing in single-dish portions removes that problem entirely.
Ice cube trays and small flat bags both work, and flat freezing has the advantage of thawing in minutes rather than hours.
Labelling matters more than it seems, because several different pastes look identical once frozen.
Why one base supports many dishes
A neutral onion-tomato paste is deliberately underspiced, so the dish-specific character is added at cooking time along with the main ingredient.
That means a single batch can become a lentil dish one evening and a vegetable or meat gravy the next, with the difference arriving in the last few minutes.
Cooks who prefer more variety keep two or three bases, typically differing in whether they contain tomato and how heavily they are spiced.
What still has to be done fresh
Whole-spice tempering does not survive storage well, since its aromatics are exactly the volatile ones. It takes under a minute and is worth doing at the pan.
Fresh coriander, green chilli, ginger julienne and lemon all belong at the end for the same reason, and they are the elements that make a reheated dish taste made rather than kept.
The result is a kitchen where the slow work happens once a week and the fast, aromatic work happens each evening.