1. In a medium saucepan, melt the butter over medium heat. Add the sliced onions and cook until they are golden brown and caramelized, about 10 minutes. Stir occasionally to prevent burning.
2. Add the rice to the saucepan, stirring for about 2 minutes until the grains are lightly toasted and coated with the butter and onion mixture.
3. Pour in the beef broth, and add the garlic powder, thyme, salt, and pepper. Stir everything together and bring to a gentle boil.
4. Reduce the heat to low, cover the saucepan, and let it simmer for about 18-20 minutes, or until the rice is tender and has absorbed all the liquid.
5. Remove the pan from the heat and let it sit, covered, for about 5 minutes to allow the flavors to meld together.
6. Fluff the rice with a fork, garnish with chopped parsley if desired, and serve warm.

I remember the first time I caramelized onions on my own; it felt like a rite of passage. The key is patience, something my abuela always emphasized. Cooking is about taking the time to let the flavors develop, and this dish is a testament to that.