Slowly melt the 1/2 measurement of dark chocolate over a double boiler or in the microwave. Once chocolate is fully melted, mix in the feuilletine.
Using an offset spatula, gently press the mixture into the bottom of the tarte shell, making sure to fill all corners. Set aside.
To make the chocolate ganache:
Slowly melt the dark and milk chocolate for the ganache over a double broiler or in the microwave. While the chocolate is melting, combine the cream and corn syrup in a saucepan and heat until just scalding.
Pour the hot cream over the chocolate in three parts, using a spatula to mix well between each addition.
Add the butter in a few small pieces and, using a spatula mix until smooth and no traces of butter remain.
To finish the tart:
Pour the ganache into the tart shell, making sure not to overfill it (there might be a bit left over). Sprinkle cocoa nibs in a decorative line over the top of the tart for added crunch.
Refrigerate the tart for at least three hours, until well set. Remove from the refrigerator about 30 minutes before serving
Storage: This tart will keep in the refrigerator for up to three days.