- Place the parsnips in a saucepan. Cover with water and add salt. Bring to a boil and cook until tender. Drain.
- In a food processor, purée the parsnips and butter. Add the milk in a thin stream and process until smooth. Strain. Refrigerate until chilled, about 45 minutes.
- In a bowl, gently combine the puréed parsnips and whipped cream. Refrigerate.
- With the rack in the middle position, preheat the oven to 260°C (500°F). Line a rimmed baking sheet with parchment paper.
- Place all the ingredients except the water on the baking sheet. Season with salt. Roast until the bones are well browned, 35 to 45 minutes, turning the bones and vegetables 3 times in the process. Remove from the oven. Transfer to a Dutch oven or stockpot, add the water and bring to a boil. Reduce the heat and simmer gently for 40 to 45 minutes. Strain and degrease.
- Warm the parsnip foam on high power in the microwave oven for about 2 minutes.
- To serve, heat the bouillon to simmering. Pour into cappuccino cups and top with parsnip foam. Grind pepper on the foam. Serve with a cappuccino spoon.