Preheat oven to 350°F (175°C).

In a large bowl, combine mashed sweet potatoes, 1 cup of sugar, and melted butter.

Add eggs, vanilla, salt, cinnamon, and ginger to the sweet potato mixture.

Mix thoroughly until well combined.

Gradually add milk while stirring continuously.

Pour the sweet potato filling into the unbaked pie crust.

Bake for 40-50 minutes, or until the filling is set.

Remove the pie from the oven and place it on a rack to cool completely.

For the meringue, beat egg whites until soft peaks form.

Gradually beat in the remaining 1/4 cup of sugar until the sugar dissolves and the mixture is glossy and stiff.

Spoon the meringue onto the cooled pie, ensuring it covers the edges.

Bake for 5-10 minutes, or until the meringue is lightly browned.