The useful ingredient in this pasta is the water you would normally pour away. Save it before draining; trying to recover it afterward is an unnecessarily dramatic end to dinner.
Cook 180 g dried egg-free pasta for two people, following the packet. In a wide pan, gently warm two tablespoons of olive oil with a finely grated garlic clove. The garlic should smell fragrant, not turn brown. Add the zest of a washed lemon and take the pan off the heat.
Toss in the cooked pasta with a little reserved water. Stir briskly, adding more water by the spoonful until the coating looks glossy rather than oily. Add lemon juice gradually: start with a tablespoon and taste. Black pepper and chopped parsley finish it.
If you want something more substantial, fold in cooked peas or white beans. Keep the sauce loose enough to coat those additions too, instead of expecting the original small amount to stretch indefinitely.
Watch the coating, not the clock
When the pasta first meets the oil, it may look glossy in patches with liquid collecting underneath. Keep tossing over very gentle heat, or off the heat if the pan is already hot. The movement matters. Add water in small amounts and let each addition join the sauce before pouring in more.
If the sauce is oily, a little water and more tossing may bring it together. If it is watery, keep moving the pasta briefly so some liquid is absorbed or evaporates. Do not leave it cooking unattended while you set the table; the right moment can pass quickly.
Taste the finished pasta with a clean fork. Lemon zest can give plenty of citrus aroma before the juice goes in, so there is no obligation to use the whole fruit. An especially sharp lemon might need only a little juice. Keep the rest for the next meal rather than squeezing it in because it is already cut.