Step 1

Preheat your oven to 375 degrees Fahrenheit. Spray or butter a 9x13 baking dish and set aside.

Step 2

To a large mixing bowl, add the sweet potatoes, sugar, maple syrup, eggs, vanilla, and salt. Using a potato masher or large fork, mash the potatoes together with the other ingredients. Once the potatoes are mashed, add the buttermilk and use a wire whisk to mix all of the ingredients until well combined.

Step 3

Transfer the sweet potato mixture to your prepared baking dish and set it aside while you make the streusel topping.

Step 4

In a medium mixing bowl, add the brown sugar, melted butter, flour, chopped walnuts, salt, and ground cinnamon. Using a fork, mix the ingredients together until all of the flour is moistened and a crumbly texture is formed.

Step 5

Spoon the streusel topping over top of the sweet potato mixture and spread out into an even layer. Bake the casserole in the preheated oven for 30-40 minutes until the casserole is golden and bubbly. Allow the casserole to cool for about 10 minutes then serve warm.