Combine the cream and glucose syrup in a saucepan. Bring to a boil.
Pour the hot cream mixture over the chopped dark chocolate and let sit for 1 minute to allow the chocolate to melt.
Using a paddle, stir the mixture in vigorous small circles in the center of the bowl until it emulsifies.
Stir outward in larger circles to spread the emulsion throughout the bowl, checking to see that all of the chocolate has melted. If necessary, heat the ganache over a hot water bath to melt the chocolate. The temperature of the ganache should not exceed 34°C/93°F.
Stream in the orange liqueur until the mixture is homogeneous.
Stir the butter into the ganache, taking care that no lumps of butter remain.
Place the ganache on marble and agitate lightly to induce crystallization.
Using a pastry bag fitted with a no. 3 star tip, pipe the ganache into rosettes on a sheet pan lined with parchment paper.
Allow the rosettes to crystallize for 30 minutes until firm, then place them in a crystallizing pan.
To Make the Syrup
Boil the sugar and water together, cleaning the sides of the pot well using a pastry brush and water. Adjust the density to 72° Brix, adding more sugar or water as necessary.
Cover the syrup mixture with a moist towel and allow to cool, undisturbed, until it reaches 23°C/74°F.
When the syrup has cooled, gently pour it into the crystallizing pan to cover the ganache rosettes. Leave undisturbed for 1 to 3 days, depending on the desired result.
Remove the rosettes from the syrup, and allow to dry on an icing screen overnight.