Place the chunked parsnips, garlic cloves, and thyme sprigs into a large pot. Cover with cold water and generously salt the water. Bring to a boil over high heat, then reduce heat to medium and cook for 15-20 minutes, or until the parsnips are very tender.
Drain the parsnips and garlic thoroughly, discarding the thyme sprigs. Return the drained parsnips and garlic to the pot off of the heat.
Add the butter, milk, salt and pepper to the pot.
Using an immersion blender, blend the mixture directly in the pot until it’s smooth and creamy. For a thinner purée, you can add more milk. Taste and adjust seasoning if necessary.
Transfer to a serving bowl, garnish with fresh thyme leaves and an additional sprinkle of black pepper and butter.
Notes
Start with the specified amount of milk. If you prefer a thinner purée, add more milk one tablespoon at a time while blending until you reach your desired texture.