01 - Preheat the oven to 350°F (175°C).
02 - Fit the unbaked pie crust into a 9-inch pie dish, crimping the edges if desired. Set aside.
03 - Combine mashed sweet potatoes, granulated sugar, whole milk, eggs, melted butter, vanilla extract, cinnamon, nutmeg, ginger, and salt in a large mixing bowl. Blend thoroughly using a whisk or electric mixer until smooth.
04 - Transfer the sweet potato mixture into the prepared pie crust. Smooth the surface evenly with a spatula.
05 - Bake in the preheated oven for 45 to 50 minutes, until the center is set and a knife inserted comes out clean.
06 - Remove the pie from the oven and allow it to cool for 10 minutes.
07 - Evenly distribute mini marshmallows over the pie surface.
08 - Return the pie to the oven and bake an additional 5 to 7 minutes, until marshmallows are puffed and golden. Monitor closely to prevent burning.
09 - Cool the pie for at least 30 minutes before slicing and serving.