Yes you get far more than one stalk per plant, but only harvest it for the 6 week period from when it is actively first producing (the month will vary depending on where you live in the world). If grown from seed do not harvest any spears for three years. If grown from crowns do not harvest spears for two years. Cut at the soil surface or just below with a serrated asparagus knife. Never be tempted to keep harvesting throughout the year or you will weaken the plants and stop the cycle (or kill the plants). Do not harvest all the stalks from any one plant, make sure to leave a good few on there to boost up the plant for the following year.
About 6 plants will produce a nice 6 week crop for a family of three or four.