1Remove the leaves from the cauliflower, slice it in half, then slice off florets from the stem. Discard the leaves and stem.
2Peel the potatoes and slice in 1/2 inch cubes.
3Bring the broth to a boil and add the cauliflower florets and the cubed potatoes. Boil the vegetables until they are tender - about 12 minutes. Remove from heat and strain.
4Place the vegetables in a food processor and process until smooth. Alternatively you can use a stainless steel food mill to puree the vegetables. Stir in the mascarpone cheese, crushed garlic, egg, pepper and nutmeg until blended.
5Spread the puree in a greased 1 1/2 to 2 quart baking dish and top with the grated cheese.
6Bake at 400°F for 15 minutes, or until golden brown and bubbly.
Stir in cooked bacon or cubed ham for an extra hearty cauliflower casserole.
Substitute broccoli florets for part of the cauliflower for a more colorful casserole.
For a different flavor, add a couple of pinches of curry or cumin.