Are to be cooked just in the same manner as carrots; they require more or less time, according to their size, therefore match them in size, and you must try them by thrusting a fork into them as they are in the water; when this goes easily through, they are done enough; boil them from an hour to two hours, according to their size and freshness. Parsnips are sometimes sent up mashed in the same way as turnips, and some cooks quarter before they boil them.
Note: Well, you can see that in this recipe MR differs from her usual vegetable cookery style and recommends a very long time to boil her parsnips. Since parsnips were a winter vegetable that could be held in the ground well after the first snows and even dug all winter through till spring perhaps she was used to very mature and large parsnips.
We, however, are fortunate to be able to get nice sized fresh parsnips in most markets. A sauté in a bit of water will tenderize the slices in 20 minutes or less whether cut long or round. Her advice to use a fork to test the cooking parsnips is spot on. Once the parsnips are tender I drizzle butter and honey on them in the pan and continue gently stirring till the edges of the pieces are beginning to brown slightly. Do not walk away from the pan at this step for the honey will burn easily. I think MR would approve of my variation.