In a nonreactive medium saucepan, combine the white wine, ham, cèpes, and shallots; bring to a boil. Lower the heat and reduce to a glaze, about 30 minutes.
Add ½ cup of the Madeira and boil down to a glaze. Add the demi-glace and simmer for 15 to 20 minutes to blend the flavors.
Strain through a sieve lined with several layers of cheesecloth, pressing d