Add diced onion to the skillet and saute on medium heat for 5-6 minute until the onions have softened and looks translucent.
Once the onions are light brown in colour, add minced garlic, thyme and salt. Saute again for 8-10 minutes on very low heat until the onion is caramelized and uniform brown in colour. If you see onion is getting stuck at the bottom towards the end, splash a few drops of water in between and keep stirring.
Toward the end add Worcestershire sauce and mix well. Let the mixture cool down completely.
In a mixing bowl, Whisk together. Add caramelized onion and mix again. Check the seasoning and add more salt or pepper if needed.