Combine ingredients of cake package as directed, as well as adding sour cream. Beat until smooth. Then add chocolate chips and work into mixture.
Bake cake as directed on package. Allow to thoroughly cool (at least 1 hour) before spreading nutella mixture onto cake.
In a small pan (like one used to boil water), place about 1/2 cup of the sliced almonds over low heat (don't use any oil or anything else, just the almonds). Roast slowly & carefully (stay by the stove and constantly mix the almonds around) for about 10-15 min. You'll know when its done when you get a slight roasty smell or just try and you should know. DO NOT OVERROAST, as if you do the almonds will burn.
Allow almonds to cool off and place over cake in whichever pattern you desire. (I've been as lazy as to just randomly scatter them or as meticulous to spell out happy birthday with the almonds, its upto you :)