Set the oven to 425°F/ 218°C (high) bake (not convection) and adjust the rack to the middle. While the oven preheats, line a baking sheet with parchment paper and set aside.

Place the sweet potatoes on the prepeared baking sheet, then transfer to the preheated oven and roast for 1 hour and 15 minutes or until fork tender. While the sweet potatoes roast, continue with the recipe.

While the sweet potatoes roast, whisk the ingredients until well combined and set aside.

Melt some of the butter and combine with the rest of the ingredients to create a crumbly topping. Set aside.

Transfer the sweet potatoes to a heat proof surface and then turn the temperature to 375°F/ 190°c (medium high). Allow the sweet potatoes to cook for 5- 10 minutes.

Once slightly cool, peel the potatoes and add to the bowl with the egg mixture.

Using a large fork or potato masher, mash the sweet potatoes until smooth.

Stir until combined.

Spread evenly.

Sprinkle the streusel topping evenly over the sweet potato mixture.

Place the casserole in the oven and bake for 20 minutes or until heated through and bubbling at the edges.

Turn off the oven and transfer to a heat proof surface and allow the casserole to cool slightly before serving.