Preheat the oven to 375°F (190°C).
Make the filling: In a large bowl, combine the mashed cranberry beans, brown sugar, milk, melted butter, eggs, vanilla extract, cinnamon, and salt. Whisk or blend until smooth.
Assemble the pie: Pour the mixture into the graham cracker crust and spread it evenly.
Bake: Cover and place the pie on the middle rack and bake for 1 hour, removing the cover after 45 minutes. (Pie is finished when the filling is just set and the center is only slightly jiggly.)
Cool briefly and serve: Let the pie cool for a few minutes before slicing. Top with whipped cream or a dusting of powdered sugar, if desired.