This vegan, savory sweet potato casserole is unique and delicious! Silky sweet potato puree is topped with caramelized onions and walnut "breadcrumbs" for a memorable, comforting dish.
Preheat the oven to 425 degrees Fahrenheit. Use a fork to poke holes all over the whole, unpeeled sweet potatoes. Rub them in a very light coating of olive oil and place on a baking sheet or in a baking dish. Roast until completely tender, about 60 minutes.
Meanwhile, caramelize the onion or shallot: warm 1 tbsp of olive oil in a wide skillet, and add the sliced onion when hot. Continue to cook over medium-low to low heat, stirring occasionally, until deeply golden and tender, about 40 minutes. Season with a pinch of salt and set aside.
You can also make the walnut crumb topping while the sweet potato and onions cook. Add all of the ingredients for the topping to a food processor, plus 2 tbsp of olive oil, and pulse until crumbly. Set the crumb topping aside and rinse out the food processor (you'll use it one more time).
Once the sweet potato is removed from the oven and cooled, remove the peel, then add it to the food processor with 1 tbsp of olive oil. Puree until very smooth. Season to taste with salt and pepper.
Lightly grease a 9x9 inch baking dish (pictured is a nonstandard 7x11 inch dish, which is about the same surface area). Transfer the pureed sweet potato into the dish and smooth it out. Spread the caramelized onion evenly on top. Finally, sprinkle the walnut crumb topping in an even layer.
Bake for about 20 minutes at 350 Fahrenheit, or until the topping is evenly browned. Be careful, the walnuts can burn quickly - start checking on the casserole at around the 10-15 minute mark. Serve warm, or make ahead and reheat!