I start by melting a knob of butter in a medium-sized saucepan. An onion and a clove of garlic, both chopped, go in next. Toss them around so they take on a buttery sheen. Then add cubed, unpeeled potatoes, one of medium size per person and one for the pot should do it. Using a wooden spoon, toss those around too. Next, into the mix goes the featured vegetable (courgettes in this case; carrots are good and leeks are excellent). Finally, throw in the thyme. Add water to cover, bring to a simmer, put the lid on the pot, the timer on for a half-hour and go sit somewhere and read.
When the timer pings, return to the kitchen and stick a sharp knife down through the vegetables to check that everything's cooked. Then whizz with a hand-held blender until the mixture is smooth.
Here's where you start tinkering. Salt and pepper of course. Maybe more water to thin the mixture. A little cream never hurts.
If you have stock on hand, you can of course use that. But, quite honestly, plain tap water is fine. Water, vegetables, herbs, salt and pepper. A lovely, comforting soup that warms you down to your toes is really no more complicated than that.