Place the chocolate chips in a small bowl and microwave for 30-seconds, then stir. Continue melting the chips using 15-second intervals until completely melted. If using a chocolate bar, chop it into small pieces the size of chocolate chips.
In a small bowl, mix the flour, cocoa powder, and salt with a wire whisk and set aside.
In the bowl of a stand mixer add the softened butter, and both sugars. Mix on medium speed until creamy.
Mix in the egg and vanilla then scrape down the sides of the bowl.
Add the melted chocolate and mix on medium speed until incorporated.
Add the flour/cocoa powder mixture in ½ cup increment and mix on medium speed just until the flour is incorporated and the dough forms.
Divide the dough in half and form it into a 6" x 2" log and place it on a piece of plastic wrap or parchment paper. The dough will be just a bit sticky. Now with your hands roll the dough back and forth and shape the log so it is the right size and nice and smooth.
Add the nonpareil sprinkles to a casserole type dish or pan that has sides to it and is large enough to fit the dough logs.
Place the just rolled dough log in the sprinkles and roll the log around until it is completely covered. You want the dough to be sticky from the heat of your hands so the sprinkles will stick to it.
Wrap the sprinkles covered dough log in parchment or plastic wrap and chill for one hour.
Repeat with the other dough log.
Preheat the oven to 350° F. and prepare two baking sheets with parchment or a Silpat
Remove the chilled dough from the wrapping and place it on a cutting board. Cut each log into ¼" slices and place on the baking sheet.
This is optional but you can place on jumbo heart sprinkle in the center of each cookie before baking.
Bake for 12-13 minutes then remove the cookies to a cooling rack.
Store the shortbreads for up to two weeks in an airtight container.