Preheat your oven to 191 °C (190 °C). Lightly grease a 9x9 inch baking dish or a similar-sized oven-safe dish.

Prepare the sweet potatoes: Wash and pierce the sweet potatoes several times with a fork. Bake them directly on the oven rack for 50-70 minutes, or until tender when pierced. Alternatively, boil or microwave them until fork-tender. Let cool slightly, then scoop out the flesh and mash it thoroughly in a large bowl.

Prepare the sweet potato base: To the mashed sweet potatoes, add the melted butter (120 ml), granulated sugar, eggs, vanilla extract, cinnamon, nutmeg, and salt. Beat with an electric mixer on medium speed until smooth and well combined. Pour this mixture into the prepared baking dish and spread evenly.

Prepare the pecan streusel topping: In a separate medium bowl, combine the brown sugar, all-purpose flour, and chopped pecans. Pour in the 80 ml of melted butter and stir with a fork until the mixture is crumbly and well-moistened.

Assemble and bake: Sprinkle the pecan streusel mixture evenly over the sweet potato base in the baking dish. Bake for 30-35 minutes, or until the topping is golden brown and the sweet potato mixture is set and lightly bubbling around the edges.

Rest and serve: Let the bake rest for 5-10 minutes before serving. This allows it to set slightly, making it easier to serve.