1. Prepare crust. Grease a 9" pie plate with butter. Combine graham craker crumbs, pecans and melted butter in a bowl and mix well. Pour mixture into pie plate a press mixture into place so that it is evenly distributed on the bottom and sides of the pie plate. Bake at 350 F for 10 minutes.
2. Prepare filling. In a mixing bowl, whisk sweetened condensed milk and egg yolks together. Add vanilla, grand marnier and lime juice. Whisk until mixture is blended. Pour into pie crust. bake at 275 F for 20 minutes. Refrigerate.
3. Prepare topping. Combine cream, sugar and vanilla in a chilled bowl and whip until stiff peaks form. Spread mixture over chilled pie. Garnish with lime slices and mint.