Place sliced strawberries in a bowl and stir in sugar. Cover and refrigerate while you make shortcakes.
Preheat oven to 350.
In a mixing bowl, combine flour, sugar, baking powder, cream of tartar, and salt. Cut cold butter into pieces and, using a pastry blender or a fork, cut the butter into the flour mixture until crumbly.
Whisk together cream and egg. Pour into flour/butter bowl and stir. Put the dough onto a work surface and lightly knead until it comes together enough to work with, but don't overwork it or shortcakes will become tough.
Roll or pat the dough into 1/2-3/4 inch thickness. Cut with biscuit cutters, cookie cutters, or a knife into the shape you desire (circles and squares are the most common). You should be able to get 6 biscuit-sized shortcakes.
Place shortcakes onto a baking sheet and bake for 20 minutes or until bottoms are golden and biscuits are cooked through. Carefully remove to a cooling rack.
!For Nutella Whipped Cream:
In the bowl of a stand mixer, with the whisk attachment, pour cream and whisk on medium-high speed until stiff peaks are just achieved.
Turn off mixer and add Nutella. Resume whisking on low speed until Nutella is just incorporated, scraping sides and bottom of bowl, being careful not to over whip.
!To Assemble Dessert:
With a straight-edged knife, slice shortcakes in half. Place bottom onto serving plate and top with a generous amount of the whipped cream and strawberries (don't forget a little of the juice). Top with the top of the cake and add a little more cream and strawberries.