Place celery root in a pan and add water to cover. Bring to a boil and simmer until soft, 5 to 10 minutes. Add peas towards the end of cooking and bring back to a simmer. Simmer until peas are tender, adding the mint leaves about 1 minute before removing from heat.
Remove pan from heat and drain, reserving about 1/2 cup of the water. Add olive oil to the vegetables and puree to desired consistency, adding some of the reserved water only if needed.
