In a bowl, season the beef cubes with 1/4 teaspoon of salt and black pepper.

Heat a heavy-bottomed pan over medium heat and add enough cooking oil to coat the pan. Add the potatoes and let them cook undisturbed until the bottom starts to brown. Then, add the thyme sprigs, 1/4 teaspoon of salt, and black pepper. Stir and cook until the potatoes are just tender, which usually takes about 5-7 minutes. Transfer the potatoes to a plate and set them aside.

Increase the heat to medium-high and add more oil to the same pan if needed. Add the beef cubes and let them sear undisturbed for about 45 seconds or until they start to develop colors. Flip the cubes and cook the other side for about 30 seconds. Add 1/2 tablespoon of butter and minced garlic, then stir and cook for a few more seconds until the garlic is fragrant.

Return the potatoes to the pan and give everything a quick stir. Slightly lower the heat and add 1 tablespoon of butter and 1 1/2 tablespoons of soy sauce. Stir to coat the beef and potatoes with the sauce and cook to your desired level of doneness. Be careful not to overcook the beef.

Adjust the seasoning to your liking. Turn off the heat and transfer the beef and potatoes to serving plates. Sprinkle with chopped parsley for a fresh touch. Serve the dish immediately and enjoy the delightful flavors.