Clean and peel the Jerusalem artichokes, and cut the larger tubers into smaller pieces.
Put them in a pot with peeled, chopped garlic, thyme, and water.
Boil the Jerusalem artichokes until tender, about 8-10 minutes.
Remove the thyme sprigs and discard them.
Roughly purée the Jerusalem artichokes with an immersion blender, add the butter, and blend until it's incorporated into the mash.
Add cream or milk in careful amounts while blending until the Jerusalem artichoke purée reaches the right consistency.
Season to taste with salt and pepper.
Serve!