Preheat your oven to 375°F (190°C).
Place the butternut squash cubes on a baking sheet. Drizzle with olive oil, and season with salt and pepper. Toss to coat evenly. Roast in the preheated oven for about 25-30 minutes or until the squash is tender and slightly caramelized.
While the squash is roasting, melt the butter in a large skillet over medium heat. Add the chopped onion and minced garlic, and sauté until the onion becomes translucent and fragrant, about 5 minutes.
Add the fresh spinach leaves to the skillet and cook until they wilt down, stirring occasionally. This should take about 3-4 minutes.
In a separate saucepan, heat the heavy cream over medium-low heat. Add the grated Parmesan cheese, dried thyme, ground nutmeg, and a pinch of salt and pepper. Stir until the cheese has melted and the sauce is smooth.
Combine the roasted butternut squash with the sautéed spinach and onion mixture. Pour the cream sauce over the vegetables and gently stir to coat everything evenly.
Transfer the mixture to a baking dish and spread it out in an even layer.
Bake in the preheated oven for 25-30 minutes or until the top is golden brown and bubbly.
Remove from the oven and let it cool for a few minutes before serving.
This creamed spinach and butternut bake makes a delightful side dish or even a vegetarian main course. Enjoy!