Preheat the oven to 375 degrees F. Line a 10 1/2 x 15 1/2-inch jellyroll pan with parchment and spray with nonstick vegetable spray.
In a dry bowl, melt chocolate over barely simmering water. Whisk the eggs and sugar until they hold a ribbon shape for 2 seconds. Whisk in the Coffee mixture. Sift, then fold in the cocoa. Fold in the melted chocolate. Spread in the prepared pan and bake for 9 minutes until set. Let cool.
Meanwhile, make the filling. Sift the cocoa and confectioners' sugar into the cream and whip to the consistency of shaving cream. Divide the sheet cake in half. Lightly spread one layer with apricot preserves. Spread on the whipped cream. Lightly spread the other half with raspberry preserves and flip on top of the whipped cream. Refrigerate.
Make the Ganache: Put the chocolate in a small bowl. Over medium heat, bring the cream to a scald. Pour the hot cream over the chocolate. Working from the center out, gently stir with a whisk to melt and blend. Continue stirring until smooth. Stir in the nibs, if using. Pour over the cake. Allow cake to chill in the refrigerator for 30 minutes, until chocolate is set.