Luckily, cooking is more forgiving than baking so not being exact is not a big problem. Try about half the sorrel you got in the share and half of a medium onion. If you have have 1/4 teaspoon measure, fill it about halfway with Worcestershire sauce. If you don’t have measuring spoons, shake the bottle once or twice into the other ingredients. If you like what you taste, you’re good to go. If not, add a bit more of things to suit your taste.