Creaminess need not contain cream. In an oil-based pasta sauce, the silky finish comes from an emulsion, a mixture in which tiny oil droplets are dispersed through water rather than floating above it. The cloudy cooking liquid, so often discarded, supplies starch that helps this arrangement last long enough to coat the pasta instead of pooling beneath it.
Starch deserves qualified credit. As pasta cooks, heat and water cause starch gelatinization, swelling starch granules and allowing some starch to escape into the pot, where it increases the liquid's viscosity. Motion does the mixing. When the pan is tossed or stirred vigorously, oil breaks into droplets, while the thicker surrounding liquid slows their movement and makes encounters between them less frequent. This is not cream. Nor is starch simply a substitute for the surfactants in egg yolk; its practical contribution is largely to thicken the water phase and discourage rapid separation.
Technique beats an extra ingredient. Reserve some cooking water, then add it gradually to the oil and nearly cooked pasta while tossing, allowing gentle heat to evaporate excess water as the sauce comes together. Concentration changes the result. Water from a smaller cooking volume generally carries more starch, whereas very dilute water may loosen the sauce without lending much body, and excessive reduction can leave it sticky or salty. Gloss is the target. On the plate, what looked like kitchen waste becomes the thin, shining boundary between a puddle of oil and supper.
