Preheat the oven to 350°F. In a large bowl, stir together the melted butter and peanut butter. Add the evaporated milk and eggs and stir to combine. Add the cornstarch, sugar, and vanilla and stir until combined and smooth.
Pour the mixture into the unbaked pie crust being cautious not to over-fill. Bake for 45 to 55 minutes or until a crust has formed completely across the top of the pie. The top will have the appearance of a peanut butter cookie. There might still be a little jiggle to the pie. Allow to cool completely before slicing and serving. This will allow it to set even more. Serve with a dollop of whipped cream, if desired.