How to Make It
Preheat the oven to 375°. Spread the sesame seeds in a pie pan and bake for about 2 minutes, or until lightly browned. Transfer the seeds to a plate to cool.
Rub the cut sides of the squash with olive oil and season with salt and pepper. Set the squash, cut side down, on a baking sheet and roast for about 25 minutes, or until tender. Scoop the flesh into a large bowl and mash into a chunky puree with a potato masher. Transfer the puree to a fine sieve set over a bowl and let drain for at least 4 hours or overnight in the refrigerator.
Return the puree to the large bowl and use a wooden spoon to gradually stir in the semolina and cornstarch. Add 3/4 teaspoon of salt and continue stirring until a soft dough forms. Divide the dough into 12 pieces. Generously dust a work surface with semolina and roll each piece of dough into a 1/2-inch-thick rope. Cut the ropes crosswise into 1/2-inch pieces. Sprinkle the gnocchi with semolina and lightly press each piece against the tines of a fork to make a ridged pattern. Dust a baking sheet with semolina and arrange the gnocchi on it in a single layer. Refrigerate for up to 4 hours.
Bring a large pot of salted water to a boil. Meanwhile, melt the butter in a large skillet. Add the sage and cook over moderate heat until crisp, about 3 minutes. Using a slotted spoon, transfer the sage to a plate. Remove the skillet from the heat.
Add the gnocchi to the boiling water and cook, stirring occasionally, until all the gnocchi float to the surface, about 4 minutes. Remove 2 tablespoons of the cooking water and reserve. Drain the gnocchi in a colander and immediately transfer them to the skillet with the butter. Season with the nutmeg and add the reserved cooking water. Cook the gnocchi until bubbling hot. Add the sage and season with salt and pepper. Divide the gnocchi among 8 soup plates. Sprinkle with the sesame seeds and serve.