Preheat your oven to 375°F (190°C). Lightly toss the sweet potato cubes with a tablespoon of olive oil, salt, and pepper, then spread them on a baking sheet. Roast for about 20 minutes until tender and slightly caramelized.
In a sauté pan, heat a drizzle of olive oil over medium heat. Add the minced garlic and cook until fragrant, about 30 seconds. Toss in the sautéed kale and cook until just wilted. Season lightly with salt and pepper, then set aside.
Pour the apple cider into a large mixing bowl. Add the roasted sweet potatoes, roasted butternut squash, and sautéed kale, gently tossing to combine. This mixture will be slightly saucy and fragrant from the cider.
Transfer the vegetable mixture into a greased baking dish, spreading it out evenly. Sprinkle the shredded cheddar cheese over the top, ensuring good coverage for a melty, golden crust.
Sprinkle the toasted sage evenly over the cheese for a fragrant, crispy topping. Place the dish in the preheated oven and bake for about 25-30 minutes until bubbling and golden brown on top.
Remove the casserole from the oven and let it rest for 5 minutes. Garnish with additional toasted sage if desired, then serve warm, enjoying the contrasting textures of creamy vegetables and crispy topping.
