❓What's the trick to making vegetable stock taste rich and savory?

The key to a flavorful vegetable stock is 'layering' multiple umami sources rather than relying on just one ingredient: dried shiitake (stems included — they're actually more flavorful), dried kelp (don't cook it too long, it turns bitter and slimy — add it near the end, or soak it separately beforehand and use the soaking liquid), corn cobs, onion skins, carrots, and soybean sprouts or soybeans, all simmered together starting from cold water on low heat for 40 minutes or more. Tomatoes bring glutamate (umami amino acids), so add one or two if you're making a stock leaning Chinese or Italian in style. Once the stock is done, portion it into ice cube trays and freeze — then just toss a cube into a stir-fry or noodle soup whenever. It's a lot more flavorful than plain water, and healthier than MSG.