stand mixer with pasta attachment or hand-cranked pasta machine
Preheat the oven to 350 degrees F. Line a baking sheet with foil. Place the squash on the prepared baking sheet and roast until easily pierced with the tip of a knife, about 1 hour. Set aside until cool enough to handle.
Cut the roasted squash in half and remove the seeds with a spoon. Scoop 2 cups of the roasted squash flesh into a food processor (reserve any extra for another use). Add the grated Parmesan and nutmeg, season with salt and pepper and process until smooth. Check the consistency of the puree; if it is slightly wet and loose, add 2 tablespoons of the flour and process again. Check the consistency and add the third tablespoon, if needed. Transfer the filling to a bowl.
Set up a pasta roller attachment on a stand mixer (or secure a hand roller on the side of your work surface). Lightly flour your work surface and roll out the dough until it is thin enough to pass through the pasta roller. Set your roller to the widest setting. Turn on the pasta roller and pass the dough through once. Fold the rolled-out piece of dough over itself, then pass through the roller again. If the edges of the dough begin to fray or the dough is sticky or damp, lightly dust both sides with flour. Repeat four or five more times, until the dough is smooth.
Adjust the roller to the second widest setting, dust both sides of the dough with flour, and pass it through twice without folding. Repeat rolling, adjusting to a thinner setting each time, until the dough is thin enough that it is slightly translucent. Once the dough gets too long to work with, cut it in half and work with one piece at a time. (Dust the resting dough piece with semolina and hold under a kitchen towel while you finish rolling the other piece.)
Dust a baking sheet and work surface with semolina flour. Lay out one sheet of freshly rolled pasta on the prepared surface. Square off the ends and trim the pasta into 4 equal-sized sheets. Spoon tablespoon-sized mounds of filling in two rows down the length of one pasta sheet, leaving about 1 inch of space between each mound. Lightly dampen the pasta around the filling (with a mister or brush) and carefully drape a second sheet of pasta over the filling to cover completely. Press firmly around each mound to squeeze out the air and seal the pasta sheets together. Trim the edges and cut the sheet into individual ravioli with a pizza cutter or rolling pasta cutter. Place the finished ravioli on the prepared baking sheet. Repeat the filling and cutting process with the remaining two pasta sheets.
Finish rolling out the remaining pasta dough and repeat the filling and cutting process. Formed ravioli may be held in the refrigerator, in a single layer and dusted with semolina, for 24 hours or frozen for up to 3 months.
Put the butter in a large saute pan over medium heat. Allow the butter to cook, stirring occasionally, until it is amber in color, 7 to 10 minutes. As soon as the butter changes color, remove it from the heat and add the sage and garlic. Set aside for the flavors to develop.
Meanwhile, bring a large pot of generously salted water to a rapid boil. Gently drop the ravioli into the boiling water and stir immediately. Leave the ravioli to cook, stirring occasionally, until tender, about 3 minutes.
Once cooked, lift the ravioli from the water with a spider or slotted spoon and add to the butter sauce with 1/4 cup pasta water. Bring to a simmer over medium heat. Hold at a simmer for 1 minute, tossing the ravioli with the sauce to coat well.
Remove the garlic clove from the sauce. Divide the ravioli between bowls, pouring some of the sauce into each. Top with lemon zest and Parmesan curls.
Mound the flour in the center of a clean countertop or cutting board. Make a well in the center of the flour 3 to 4 inches wide.
Crack the eggs into the well and add a pinch of salt. Using a fork, break the yolks and begin to beat the eggs as you would if making scrambled eggs.
Continue stirring the eggs with a fork in large circles, slowly incorporating the flour. When the eggs form a thick mass and become difficult to stir, about 3 minutes, fold the loose flour from the edges into the pile with a bench scraper and knead until a smooth dough forms. Discard any excess flour.
Shape the dough into a flat disk, wrap tightly with plastic wrap and set aside to rest for 20 minutes before rolling. If waiting more than 1 hour, refrigerate or freeze the dough. The dough will keep refrigerated for up to 24 hours.
If you don't have semolina, you can use 10 ounces of only "00" or all-purpose flour instead of 7 ounces flour and 3 ounces of semolina flour.