Preheat oven to 375.
In a medium bowl, combine pecans, brown sugar, and melted butter and mix well.
Press into 9" pie pan.
Bake at 375 for 8-9 minutes until just set.
Cool on wire rack until completely cooled.
In large bowl, combine cream cheese, cocoa powder, and 1 cup sugar.
In medium bowl, combine heavy cream and powdered sugar until stiff peaks form.
Beat a spoonful of this mixture into the chocolate mixture to lighten.
Then fold remaining whipped cream into chocolate mixture to combine.
Pour into cooled pie shell.
Cover and chill until firm, about 4-6 hours.