Rinse and chop cauliflower into bite size pieces.
Place cauliflower in a large pot of boiling (salted-add about 1-2 teaspoons) water. Cook the cauliflower until very soft, 12 to 15 minutes; drain and set to the side.
Meanwhile, in a frying pan, melt 2 tablespoons butter over medium heat. Add the leeks and garlic. Cook, stirring occasionally, until the leeks are translucent and very soft, about 8 minutes.
Using a blender or food processor (*you may have to work in batches) add the cooked cauliflower, leek mixture, salt, pepper, and heavy cream. Puree for 1 minute or until smooth in texture.
Using the frying pan from the leek mixture melt the remaining 1 tablespoon butter over medium heat. Add the panko and parsley and toast until golden in color. Top the puree with the toasted panko. Divide evenly among plates and enjoy.