Preheat oven to 350°F. Center pie crust in pan on a baking sheet.
In a medium size mixing bowls, use a whisk to sift together sugar, brown sugar, cocoa, flour and salt
In a microwave safe bowl, melt together butter and chocolate on 50% power stopping to stir every 20 seconds. Repeat until smooth.
Whisk milk, eggs and vanilla into melted chocolate. Once combined, add wet ingredients to dry ingredients mixing until fully incorporated. Pour into pie crust.
Bake for 45 -55 minutes or until the center still has slight movement when gently shaken. Check at 30 minutes and tent loosely with foil to prevent over browning.
Cool completely on a cooling rack then chill thoroughly.
Cut into desired size pieces and serve with whipped cream or vanilla ice cream.