Preheat oven to 300ºF. Heat the oil in a wide pot over medium-high heat. Pat the beef dry and season liberally with salt and pepper. Cook in batches in an even layer until very well-browned, about 4-5 minutes per side. Transfer to a bowl and set aside.
Cook the Aromatics:
Melt the butter into the pot and add the onions. Cook, stirring regularly, for 4-5 minutes until softened. Add 1 cup of the beef stock and scrape up all the browned bits stuck to bottom of the pot. Bring to a boil and stir occasionally for 4-5 minutes until reduced slightly. Add the remaining beef stock.
Return the beef back to the pot and reduce heat to low.
Add the thyme, garlic halves (cut-side up) and the red Fresno pepper. Squeeze the juice from both orange halves over the beef and add the orange halves to the pot. Taste and season lightly with salt, pepper, and crushed red pepper. Turn the heat off and cover the pot. Transfer to the oven for 2-3 hours until the beef is very tender.
Cook the Carrots:
Return the pot to the stove over medium heat. Remove and discard the orange and chili pepper. Remove the garlic from the pot. Once cool enough to handle, pop the cloves from the paper and mash them into a paste. Work the garlic paste back into the broth. Taste and season to your preferences. Add the carrots and cook, covered, for 15-30 minutes on low heat until tender. Remove the cover and cook for 5-10 minutes over medium heat to allow the sauce in the pan to thicken.
If needed, add a splash or two of water. If a thicker gravy is desired, add a flour slurry to the pan and whisk it in and allow it took for an additional 5-10 minutes to thicken.
To Serve:
Ladle the beef stew over mashed potatoes or your accompaniment of choice. Garnish with parsley, if desired. Enjoy!