Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the mashed sweet potatoes and pureed navy beans.
In another bowl, beat the eggs and add them to the sweet potato-bean mixture.
Stir in the brown sugar, vanilla extract, cinnamon, nutmeg, and salt.
Gradually add the melted butter and milk, mixing until well combined.
Pour the filling into the unbaked pie crust.
Place the pie on a baking sheet to catch any spills and bake in the preheated oven for 45-50 minutes, or until the pie is set and a toothpick comes out clean when inserted into the center. Allow the pie to cool before serving.