Make Whipped Cream. In the bowl of an electric mixer fitted with the whisk attachment, whip the cold heavy cream, granulated sugar and vanilla extract until stiff peaks form. Do not over beat. Divide half of the whipped cream into serving cups and reserve half of whipped cream to make nutella mousse later.
Prepare Bananas. Peel off the skin and cut bananas into 1/4-inch thick slices. Place banana slices evenly onto the whipped cream layer of each serving cup.
Make Nutella Mousse. Place Nutella in a small bowl and microwave for 15-20 seconds until slightly warm and spreadable consistency. Let it cool for 3-5 minutes. Gently fold the reserved whipped cream in step 1 into the nutella until combined. Divide evenly between serving cups on top of the bananas. Garnish with chopped pecans or your choice of nuts.
Place mousse in the refrigerator to set for at least 2 hours.
Keep mousse in the fridge, covered with plastic wrap, for up to 3 days.