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1
Preheat the oven to 375 degrees F.
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2
Heat the olive oil in a large skillet over medium-high heat (use a skillet with a lidyoull need it in a bit).
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3
Add the onion and cook for 3 to 4 minutes, until softened.
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4
Add the garlic and cook for about 30 seconds, until fragrant.
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5
Add the butternut squash, rosemary and nutmeg and season with salt and pepper.
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6
Mix to combine.
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7
Add the vegetable broth, then reduce the heat to medium-low and cover the pan.
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8
Cook for 15 to 20 minutes, until the squash is very tender.
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9
Remove from the heat and, using a potato masher or fork, mash the squash mixture until smooth.
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10
Transfer to a large bowl and stir in 1 cup of mozzarella, 1 cup of Parmesan, the Fontina and the ricotta cheese.
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11
Bring a large pot of salted water to a boil.
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12
Add the pasta and cook for about 6 minutes, until almost al dente.
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13
Drain the pasta and add it into the squash mixture.
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14
Meanwhile, heat the butter in a medium saucepan over medium heat.
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15
Add the flour and cook for 2 minutes.
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16
Slowly add the milk, whisking constantly until smooth.
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17
Cook for 4 to 6 minutes, stirring constantly, until the mixture thickens enough to coat the back of a wooden spoon.
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18
Stir in the mustard and season with a dash of salt and pepper.
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19
Add the sauce into the pasta and squash mixture and toss to combine.
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20
Pour the mixture into a 13 by 9-inch baking dish.
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21
Sprinkle the remaining 1/2 cup of mozzarella and 1/2 cup of Parmesan cheese over the top.
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22
Cover the dish loosely with aluminum foil and bake for 45 minutes.
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23
Remove the foil and bake for another 15 to 20 minutes, until golden brown and bubbly.
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24
Remove from the oven and let it rest for 10 minutes before serving.
