Cut the stem from a very large head (or two smaller heads) of cauliflower and remove the leaves. Slice as best as you can into 6 ca. 1-inch slices. I can usually get 4 full slices to hang together and then the remaining pieces just need to be collected.
The slices and pieces are laid out on a baking pan covered with oiled parchment, then sprayed with oil and dusted with ground black pepper. Roast at 450 F for 15-20 minutes on one side. Use a large spatula and turn over all of the pieces, spray with oil and roast another 15-20 minutes, until tender and golden brown. Remove and reduce the heat to 350 F.
Brown the Italian sausage. Near the end of the browning, add and mix the garlic, then add fennel seeds, and rosemary leaves. Heat for a few moments until aromatic and then reserve (use a slotted spoon and keep the fat in the pan).
Caramelize the onions in the hot sausage fat. About half way through the process add the red pepper. Add more herbs as desired. Near the end, combine with the sausage. Heat and mix thoroughly. Reserve.
My Italian red sauce is posted elsewhere. Caramelize two diced sweet onions with a diced red pepper. Add these to a food processor with a large can of DOP San Marzano tomatoes, a roasted red pepper, a can of tomato paste, EVOO, herbs and spices to preference. Process together and simmer on low for an hour.
Carefully remove the cauliflower to line the bottom of a 9 x 13 inch baking dish. Coat the cauliflower with tomato sauce.
Place the pieces of mozzarella in a layer. Then sprinkle the open spots with the feta.
Top with the sausage mixture.
Bake at 350 F for 25-30 minutes until the liquid is bubbly. Top with some shredded asiago about 5 minutes before the end.
Remove and let sit for a few minutes. Plate your serving with some added asiago and a sprinkle of Italian seasonings.