French Dip Sandwich

Method

1. Melt 1 tsp of the butter in a small saucepan over medium heat. Add 0.5 of thinly sliced onion with a pinch of salt and cook 5 minutes, stirring, until soft and just beginning to colour at the edges.
2. Stir in 1 clove of crushed garlic and cook 30 seconds until fragrant, then pour in 200 ml of beef stock and 0.5 tsp of Worcestershire sauce. Add 1 sprig of thyme and 1 bay leaf.
3. Bring to a bare simmer and cook uncovered for 12 minutes, until the jus has reduced by about a quarter and tastes clearly beefy. Strain into a small jug or dipping cup, discarding the aromatics, and season with salt and freshly ground black pepper. Keep hot — the jus must be steaming when the sandwich is served.