Spread 3 x 900 g portions of chocolate genoise onto 3 Flexipats®. Bake in a 160°C convection oven for approximately 12 minutes and let cool. Place between two baking sheets and refrigerate overnight so that the genoise is moist and of even thickness.
Coat the crust side of one sheet of genoise with dark chocolate. Imbibe the crumb side of this sheet with 300 g of rum syrup. Imbibe the two other sheets of genoise on the crust side, then place in the freezer.
Place the first sheet of chocolate-coated genoise in the frame. Pour in 1800 g of Namelaka, smooth, then top with the second sheet of genoise. Even out the surface, then pour in another 1800 g of Namelaka. Smooth, then top with the third sheet of genoise (crumb side up). Place in the freezer.
Spread 600 g of Namelaka in a 25 x 26.5-cm frame. Create a wavy motif using an angled palette knife, remove the frame, tap the baking sheet to even out the edges, then place in the freezer. Cut into 17.5 x 4-cm rectangles perpendicular to the wavy motif. Spray with the dark chocolate mixture.
Remove the entremets from the frame. Cut into 20 x 6.5 cm rectangles. Spray with a light coating of mirror glaze. Sprinkle the tops of the entremets with decorative icing sugar then place a rectangle of chocolate-coated Namelaka on top. Pipe out 5 dots of Namelaka using a plain 6-mm nozzle then top with the dark chocolate chips.