Place the chopped semisweet chocolate in a medium bowl. Line a baking sheet with wax paper.
Warm the heavy cream in a small saucepan over medium-low heat just until warm. (Do not let it boil.)
Pour the warm heavy cream over the chopped chocolate and let it sit for 1 minute. Stir together the chocolate and heavy cream until all of the chocolate has melted and the mixture is well combined. Stir in the Nutella, and then cover the bowl with plastic wrap and refrigerate it for 2 hours until the mixture is firm but pliable.
Remove the mixture from the refrigerator and using a spoon, scoop 1 tablespoon of the mixture from the bowl and quickly shape it into a football by rolling it in the palms of your hands. (The less you handle the mixture, the better, as the warmth of your hands will cause the mixture to soften.) If the mixture becomes too soft, place it back in the refrigerator.
Place the chocolate footballs on the wax paper-lined baking sheet. Refrigerate the footballs for 30 minutes.
While the footballs chill, melt the milk chocolate in a double-boiler or in the microwave, stirring at 20-second intervals, until it's fully melted. Set it aside for 5 minutes to cool slightly.
Remove the chocolate footballs from the refrigerator and, one by one, dip them into the melted chocolate. Return the coated footballs to the wax paper-lined sheet tray and let them sit until the chocolate coating hardens.
Once the chocolate coating has hardened, scoop the frosting into a pastry bag fitted with a small, round pastry tip and pipe the stitching onto each football. (Alternately, use a sealable plastic bag and snip the tip then pipe accordingly.) Let the frosting harden for 5 minutes then serve.