Prep the oven and pan: Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish or a similar casserole dish.
Cook the sweet potatoes: Place the cubed sweet potatoes in a large pot.
Cover with cold water by about an inch and add a pinch of salt. Bring to a boil, then reduce to a simmer and cook until very tender, 12–15 minutes. Drain well.
3 pounds sweet potatoes, peeled and cubed
Mash the base: Return the sweet potatoes to the warm pot. Add butter, Greek yogurt, maple syrup, vanilla, cinnamon, nutmeg, and salt. Mash until smooth. Taste and adjust sweetness or salt.If using the egg, let the mixture cool a minute, then stir it in.
2 tbsp unsalted butter or coconut oil, ⅓ cup plain Greek yogurt, 3 tbsp pure maple syrup, 1 tsp vanilla extract, ½ tsp ground cinnamon, ¼ tsp ground nutmeg, ¼ tsp fine sea salt, 1 beaten egg for extra lift and structure
Make the topping: In a small bowl, combine oats, nuts, almond flour, maple syrup, melted butter, cinnamon, and a pinch of salt. Stir until craggy and evenly moistened.
½ cup old-fashioned rolled oats, ½ cup chopped pecans or walnuts, 2 tbsp almond flour, 1 tbsp maple syrup, ½ tbsp melted butter or coconut oil, 1 Pinch of cinnamon and sea salt
Assemble: Spread the sweet potato mixture into the prepared dish. Sprinkle the oat-nut topping evenly over the surface.
Bake: Bake for 25–30 minutes, until the topping is lightly golden and the casserole is warmed through.
For extra color, broil for 1–2 minutes at the end, watching closely.
Rest and serve: Let the casserole rest for 10 minutes to set. Add a light drizzle of maple syrup or a pinch of flaky salt if you like, then serve warm.
For serving: A drizzle of maple syrup, flaky salt, or a sprinkle of pomegranate arils