Asparagus bunches can vary widely in size, and of course you may wish to serve more or less depending on what else you are serving. Jason and I will split an entire bunch between us, but your guests may not be as ravenous. My rule of thumb is that a large handful of stalks will serve one person. I prefer the "skinny" asparagus because they get a little more crispy, but larger asparagus are also delicious prepared this way.
You will need:
a sheet pan or shallow roasting pan
Preheat your oven to 400 degrees. Wash the asparagus and trim away any dense, woody ends.*
For easier cleanup, line your pan with foil. Toss the asparagus in a little oil -- about 1-2 tablespoons per bunch -- and sprinkle generously with salt. Add pepper to taste. Spread the asparagus out on the pan so that the spears overlap one another as little as possible. This will promote browning.
When the oven has reached 400 degrees, place the asparagus in the oven. During the cooking, open the oven as little as possible -- use your oven light -- and do not stir the asparagus. It usually takes about 20-30 minutes to cook the asparagus, depending on the thickness. If you need your asparagus done more quickly than that, just preheat your oven to 450 or higher instead -- I find that it tends to be a little less tender, but is still good when cooked at a higher temperature. When the spears are tender and browned, remove and serve immediately. (How do you tell if they're tender? Pick one up by the end with a pair of tongs. If it flops, it's tender. If it's still rigid, it's not done.)
Unfortunately, the asparagus doesn't really regain its crispness when reheated as leftovers, but we rarely fail to polish it off. If you do have some left over, it's excellent chopped and mixed into risotto along with a little lemon zest and parmesan -- but that's a recipe for another day.
*Generally, asparagus recipes recommend you trim quite a bit of the end by bending the asparagus until it snaps and discarding the stem. The roasting process tenderizes the asparagus so well that you do not need to discard as much of the vegetable -- if you are using thick asparagus spears, trim 1-1 1/2 inches of the stem end, if you are using thin, just trim the last 1/2 inch to an inch.