Prepare 2 ounces (50 grams) finely chopped mirepoix, which should include one-quarter unsmoked cured ham, such as Prosciutto di Parma (use the ends to save money). Combine the mirepoix with 7 fluid ounces (200 milliliters) Champagne or white wine. Reduce the mixture by half. Add 6 tablespoons (90 milliliters) Mushroom Essence. Add 2 cups (500 milliliters) demi-glace. Simmer the sauce gently for 10 minutes, skimming any froth that floats to the surface. Strain through a fine chinois. Put the strained sauce in a clean saucepan and reduce it to the desired consistency. Strain through a fine chinois.