Preheat the oven to 475°F. Bring a pot of salted water to a boil for the gnocchi.
Preheat a large cast-iron skillet over medium-high.
Cut the neck off the squash; peel and cut into 1- to 1 1/2-inch cubes.
Add the olive oil to the skillet and heat up the sausage, stirring occasionally and breaking it up into bite-size pieces, until browned. Using a slotted spoon, transfer the sausage to a bowl.
Add the butter to the skillet and melt then add the sage; fry until crispy and the butter browns, about 2 minutes. Using a slotted spoon, transfer the sage to a paper towel.
Add the garlic to the skillet; stir until fragrant, 1-2 minutes. Add the squash; season with salt, pepper and nutmeg.
Add the wine and cook, stirring often, until reduced a bit, about 1 minute.
Add 1 1/2 to 2 cups stock, depending on how saucy you want the dish to be, and bring to a bubble.
Add the sausage then transfer skillet to the oven. Roast until the squash is tender, 12-15 minutes.
Toss in a bag of spinach during the last minute the dish is in the oven.
Add the gnocchi to the salted boiling water and cook until they float to the surface, about 3 minutes.
Drain and toss with the squash and sausage sauce; season. Top with the sage leaves. Serve with the grated cheese.