- In a medium sized skillet or cast iron pan, heat oil over medium high heat. Cut the ends off of the red onions, remove outer skin, cut in half, then cut lengthwise in 1/4 inch slices. Add them to the hot oil in the pan. Season with salt and pepper. Reduce heat to medium and cook onions for 25-30 minutes, stirring occasionally, until they are soft with a golden brown color.
- Add Worcestershire sauce, brown sugar, balsamic glaze, 1 tablespoon fresh thyme leaves, and beef broth. Bring onion mixture to a boil on high heat. Reduce to a simmer and cook until the liquid is almost all evaporated, about 20 minutes, or until the mixture is a jam like texture. Season with salt to taste. Turn off heat and set aside to let cool.
- Preheat oven to 375 degrees. On a half sheet pan, place the phyllo cups. In each cup, app 1 tablespoon of onion mixture. Take the gruyere block and grate enough cheese on each cup to cover. Bake in oven for 15 minutes or until the onion mixture is bubbly and the cheese in caramelized. Garnish with fresh chopped thyme and serve.