Preheat oven to 350°F and lightly grease an 8x8 baking dish.

Peel and chop sweet potatoes, then boil until tender, drain well, and mash; you should yield about 4 cups of mashed sweet potatoes.

Whisk together granulated sugar, brown sugar, eggs, cream/milk, melted butter, vanilla, and salt. Combine this mixture with the mashed sweet potatoes and mix until smooth; then pour into the prepared baking dish.

For the topping, combine brown sugar, flour, cinnamon, salt, and pecans. Add softened butter and use your fingers to blend until the mixture resembles wet sand.

Sprinkle the streusel topping evenly over the sweet potatoes and bake for 30-40 minutes until golden brown.