Melt butter in a skillet over medium low heat. Add eschalot and cook for 4 - 5 minutes, until softened and sweet. Do not allow to colour.

Add vermouth and turn the heat up to medium-high. Let it simmer, scraping the base of the pan to dissolve any fond (stuck caramelised bits) into the liquid, until the liquid is almost totally evaporated. The alcohol cooks out during this step.

Add beef stock and let it simmer for 6 to 7 minutes until it reduces by 3/4 (exact time will differ depending on stove strength and pan size).

Add cream and simmer for a further 4 minutes or until it changes from a pale cream colour to a medium brown colour.

Season with salt and pepper, and taste to adjust.

Strain sauce through a fine mesh strainer into a bowl. If you have much more than 100ml / 3.5 oz jus once strained, then return to pan and simmer on low for a bit longer.