Preheat the oven to 425°F. Toss the cubed squash with olive oil, salt, and pepper on a large baking sheet. Spread in an even layer — don't crowd them or they'll steam instead of roast. Roast for 30-35 minutes until tender when pierced with a fork and lightly caramelized at the edges.
While the squash roasts, melt the butter in a large skillet over medium heat. Add the garlic and cook for about 30 seconds until fragrant but not browned — you want it golden, not burnt.
Carefully pour in the whiskey to deglaze the pan (it will sizzle). Let it simmer for 1-2 minutes, scraping up any bits from the bottom of the skillet. The alcohol smell will mellow and leave just a warm, slightly sweet note.
Pour in the heavy cream and bring to a gentle bubble. Simmer for 3-4 minutes until the sauce thickens enough to coat the back of a spoon (about 165°F if you're using a thermometer — it should be hot but not boiling hard). Stir in the Parmesan until melted and smooth.
Add the spinach and cook for about 1 minute, just until wilted. Season with salt and pepper.
Meanwhile, bring a large pot of generously salted water to a boil. Cook the gnocchi according to package directions — store-bought usually takes only 2-3 minutes. They're done when they float to the surface. Drain well but don't rinse them.
Toss the cooked gnocchi directly into the skillet with the sauce. Add half the roasted squash and gently fold everything together until coated. Transfer to serving dishes, top with remaining squash, a generous handful of toasted walnuts, and torn basil leaves. Serve immediately while hot.
