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1
Preheat oven to 350F.
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2
Coat 10-inch springform pan with cooking spray.
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3
Bring large pot of salted water to a boil with fresh sage sprigs; use this boiling water to separately blanch mushrooms (3 minutes), then leeks (2 minutes), and then broccoli (1 minute).
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4
Immediately transfer each vegetable to colander with slotted spoon, rinse under cold water, drain well, and transfer to 1 large bowl.
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5
Cook rigatoni in boiling water 3 minutes less than cooking time recommended on package, then drain, rinse under cold water, and transfer to separate large bowl.
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6
Melt butter in large saucepan over medium heat.
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7
Add flour, and cook 3 to 5 minutes, or until beginning to turn light brown, stirring constantly.
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8
Add butternut squash soup, and cook 5 minutes, or until thickened, stirring constantly.
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9
Stir in 1 cup grated cheese, chopped sage, and 1 tsp.
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10
truffle oil (if using); season with salt and pepper, if desired.
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11
Stir soup mixture into pasta, add blanched vegetables, and stir to combine.
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12
Spread one-third of pasta mixture in prepared springform pan; dot with 1/3 cup ricotta cheese.
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13
Repeat twice with remaining pasta mixture and ricotta, and then sprinkle with remaining 1 cup grated cheese.
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14
(If making ahead, cover springform pan tightly with foil, and refrigerate up to 24 hours.
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15
Uncover before baking.)
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16
Place springform pan on large baking sheet, and bake 30 minutes, or until top is browned and cheese is melted.
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17
Let stand 5 minutes before unmolding and serving.
