Preheat the oven to 350°F [180°C]. Line two baking sheets with parchment paper.

In a small bowl, combine the flour, cocoa powder, cacao nibs, and salt. Set aside.

In a large bowl, with a hand mixer, beat together the butter and granulated sugar until light and fluffy, about 3 minutes. Add the egg and beat until smooth. Gradually beat in the flour mixture until the dough comes together in a ball. Form the dough into a disk, wrap tightly with plastic wrap, and refrigerate for at least 1 hour, or up to 4 days. (The dough can also be frozen for up to 3 weeks. Defrost in the refrigerator overnight before using.)

Preheat the oven to 325°F [165°C]. Set aside a 4‑by‑13‑in [10‑by‑33‑cm] or 9‑in [23‑cm] tart pan.

On a lightly floured work surface, roll out the chilled dough to 5 by 14 in [12 by 35.5 cm] or a 10‑in [25‑cm] round, dusting with a little more flour as needed to keep it from sticking. If the dough gets too sticky, put it back in the refrigerator for about 15 minutes and add a little more flour to your work surface. Roll the round of dough onto the rolling pin and carefully unroll the dough into the tart pan. Press the dough down into the bottom of the pan and up the sides. Using a fork, poke holes in the dough to keep it from puffing up too much while baking.

Bake the crust for 6 to 8 minutes, or until the dough is puffed and slightly darker around the edges. The crust will still look a little doughy in the center, but it will set as it cools. Let cool completely on a wire rack.

When the crust is cool, pour the ganache into the shell and spread it out evenly. Set aside.

In a large bowl, with a hand mixer, beat together the cream cheese, superfine sugar, and cocoa powder until combined, thick, and fluffy, about 3 minutes. Pour the filling into the crust and spread it evenly over the ganache. Place the berries on the top in any design you’d like. Refrigerate the tart for at least 1 hour, or overnight, then slice into wedges and serve. Store in an airtight container in the refrigerator for up to 2 days.