Sweat 3 ounces (75 grams) mirepoix in butter until it starts to soften. Break up 1 pound (500 grams) game meat or fowl trimmings into ½-inch (1 cm) pieces with a cleaver or heavy knife and add them to the mirepoix. When the trimmings begin to brown, add 5 fluid ounces (150 milliliters) white wine and reduce by two-thirds. Add 1¾ cups (450 milliliters) demi-glace. Cook for about 45 minutes to extract the flavor from the trimmings and mirepoix. Strain the sauce, first through a coarse chinois, then through a fine chinois. Add 7 fluid ounces (200 milliliters) appropriately flavored stock to the strained flavor base. Reduce if necessary to thicken. Finish the sauce by whisking in 2 ounces (60 grams) butter. Season with salt and pepper.