Preheat oven to 350°F (175°C). Place pie crust into a 9-inch pie pan.
In a large bowl, mix sweet potatoes, sugars, evaporated milk, eggs, vanilla, cinnamon, nutmeg, and salt until smooth.
Pour filling into pie crust and smooth the surface.
Bake for 45 minutes.
While baking, prepare the topping: melt butter in a saucepan, stir in brown sugar, flour, vanilla, and salt. Cook 2–3 minutes until thickened.
Fold in chopped pecans and remove from heat.
After 45 minutes, remove pie and sprinkle praline topping evenly over it.
Return to oven and bake another 15 minutes, until topping is golden and bubbling.
Let cool completely before slicing.