Bake them in a 325 degree oven for 30 minutes. You can place them directly on the rack or use a muffin tin, which makes it easy to move them in and out of the oven in bulk. Once the 30 minutes have passed, remove the eggs from the oven (carefully, because they are hot) and plunge them in cold water for 10 minutes.
The shells may have brown spots where they were in contact with hot metal. Sometimes that discoloration fades away in the water plunge, but sometimes it will leave marks on the whites.