Crust: Preheat oven to 350°. Combine graham-cracker crumbs, butter, and 3 tablespoons sugar in a medium bowl; mix well. Press into a 9-inch pie plate, and bake until lightly browned, about 12 minutes. Remove from oven, and transfer to a wire rack until completely cooled.
Filling: In a large mixing bowl, beat the egg yolks until they are light yellow. Gradually beat in sweetened condensed milk until thickened. Gradually add lime juice and beat until smooth. Stir in sour cream and zest. Pour into cooled pie crust. Bake 15 minutes. Remove from oven.
Meringue: In a mixing bowl with an electric mixer, beat the egg whites and salt until foamy. Add the cream of tartar and beat until soft peaks form. Add the sugar 1 tablespoon at a time, and beat until stiff, glossy peaks form.
Spread over hot pie, carefully sealing to edge of crust to prevent meringue from shrinking. Use the back of a spoon to create peaks and swirls.
Bake an additional 15 minutes or until meringue is lightly browned. Cool 1 hour on wire rack. Chill at least 3 hours before serving.
Mango Coulis: In a blender, puree mango, sugar, lime juice and zest until smooth.