Cut apart the cauliflower into florets and boil in a large sauce pot until very tender.
Meanwhile, in a saute pan, with 1 Tbl of the butter and 1 Tbl of olive oil, saute the shallots and the mushrooms. Add the sun dried tomatos and keep warm over low heat.
Using a spider or slotted spoon, transfer the cauliflower to a blender (do not discard vegetable stock!)
To the blender, add the milk, salt, pepper, grated parmesan and 1 to 1-1/2 Cup of the vegetable stock. You'll need more or less depending on the size of the cauliflower. Reserve the remainder to thin out if necessary. Blend until smooth. Transfer to a pan to keep hot while pasta is cooking. Add parsley.
Serve the sauce over pasta and top with the mushroom mix. Add more cheese and garnish with parsley, if desired.