First separate out the plants that didn't bolt, and cure them as usual (in a warm, dry place for several weeks). With the bolted ones, a lot of times you can pull away the seed stalk to get a salvageable onion that won't store long but is fine for cooking for several weeks. You can do this now or later, no hurry if the onions are basically sound and kept dry.

I can keep my bolted onions for around a month before the stalk get too pithy inside to bother dealing with them. Like planatus say's you can work around it, but after about a month some black mold can start to form in there.

Right out of the ground the center stalk is still really tender, so I usually eat or sell those ones right away without curing.
-Mark