Start by making the chocolate opaline. Combine the fondant sugar and glucose in a saucepan and bring to a boil. At 135°C, add the dark chocolate and stir until fully incorporated. Continue heating until the mixture reaches 155°C. Pour the hot mix onto a silicone baking mat and let it cool completely. Once solid, break it into pieces and grind into a fine powder. Dust this chocolate powder over one side of the Nerva Tuille Mold. Mix the egg white, icing sugar, melted butter and flour until smooth. Spread a thin, even layer of the tuille batter into the other side of the mold. Bake at 170°C for 3 to 4 minutes, or until golden and crisp. Let the sheets cool slightly before unmolding them carefully. Tip: You can experiment with different chocolates, add flavoring powders to the opaline, or try alternative batters for different textures.