In a pot heat the butter and saute the onion until translucent.
Add the garlic and saute for another minute.Add the ground fennel and mix.
Add the potatoes and fennel and cover for a minute.
Add milk, water, salt and pepper.
Once it comes to a boil, cover , reduce the heat and continue to cook for about 15-20 minutes until the potatoes and fennel are fully cooked.
Check the seasonings.Carefully transfer into a blender or use a hand blender and blend until all smooth.
Garnish with some fennel fronds and serve hot.