In a medium {cold} saucepan, stir cocoa, sugar and cornstarch together. Slowly whisk cold milk into dry ingredients to prevent lumps from forming. Place on medium high heat and whisk continually.
Once pudding starts to come to a bubble, boil for 15-30 seconds or until noticeably very thick {keep whisking!}. Remove from heat and whisk in vanilla and nutella until smooth.
Pour into pie shell and cover with plastic wrap directly on filling. Refrigerate 2-3 hours or until filling is set and plastic wrap comes off clean.
In a stand mixer, whip all ingredients together until stiff peaks form. Spread cream over pie and serve cold.
Notes
*Cornstarch acts as a stabilizer for cream, so if you are making this pie in advance, I’d recommend adding the cornstarch so your cream stays firm. If you are serving immediately, then the cornstarch is optional.