Place parsnips and fennel in a large pot. Cover with just enough water to cover and season with salt. Bring to boil over medium high heat. Reduce heat and simmer for 30 to 40 minutes until soft.

Remove from heat. Strain ¾ of the liquid. Transfer vegetables to a high speed blender and puree until smooth. Taste and adjust seasoning if needed. Serve alongside Slow Cooked Sous Vide Lamb with Mint and Pistachio Gremolata.