Preheat oven to 325°F.
Combine spice blend in a small bowl and reserve.
Spread walnuts on a baking sheet and transfer to oven to toast. Remove and raise heat to 425°F.
Cut the top off the garlic bulb to expose cloves. Drizzle with oil and wrap in foil. Place squash on a baking sheet, drizzle with oil and season with about half of the spice blend. Place foil-wrapped garlic and squash in the oven and roast about 40-45 minutes until the garlic is soft and the squash is tender. Cool to handle.
Squeeze garlic cloves from their skins into a small bowl and paste; reserve. Scoop squash flesh from skin and purée in a food processor; reserve.
Bring stock with Parm rind to a simmer in a saucepot over medium heat. Reduce heat and keep warm.
Heat a drizzle of oil, half a turn of the pan, in a round-bottomed pan or a risotto pot over medium-high heat. Add sausage and brown and crumble; remove to plate. Add about 2 tablespoons oil to the pan along with the onions. Stir to soften, 3 minutes, then add rice and season with remaining spice blend. Toast rice a minute or 2 then add wine. Stir to evaporate then add roasted garlic paste and about 1/3 of the stock. Stir vigorously, letting the stock absorb fully before repeating the process until stock is incorporated, about 18 minutes.
In a small pan, melt butter. Add sage leaves and brown butter while sage leaves crisp; remove leaves to paper towel.
To finish risotto, stir in the squash purée, 3/4 of the walnuts, the brown butter, cheese and half of the sage, crumbled.
Serve risotto in shallow bowls garnished with remaining walnuts and crumbled sage.