Preheat oven to 350 degrees F.
In a large microwavable bowl, heat half and half, butter, and semi-sweet chocolate until melted.
Cool for 5 minutes.
Add sugar, brown sugar, eggs, egg yolk, and vanilla and beat until smooth.
Add cocoa, flour, and salt and mix until well blended.
Pour into the pie crust and bake for 50 to 60 minutes, or until toothpick comes out clean.
Cool and serve with ice cream and hot fudge.
