Peel the radishes and cut them into 1-inch squares approximately 1/4-inch thick. Slice the beef into thin 1/8-inch bite-sized strips. Mince the garlic freshly. Slice the mushrooms into bite-sized pieces. Cut the green onions diagonally into 1-inch pieces. Having everything prepped before cooking ensures smooth execution and prevents the soup from overcooking while you're still cutting ingredients.

Heat the sesame oil in a large pot over medium-high heat until shimmering. Add the sliced beef and cook for 2-3 minutes, stirring occasionally, until the meat is mostly cooked through but still slightly pink in the center. The beef will finish cooking in the broth, so don't overcook it at this stage. I find that searing the beef first builds a deeper flavor foundation for the entire soup.

Add the prepared radish squares from Step 1 to the pot with the seared beef and stir constantly for 2-3 minutes to lightly toast them. This helps develop the radish's subtle sweetness. Pour in the 7 cups of water and bring to a boil over high heat. Once boiling, add the minced garlic, reduce heat to medium, and gently simmer for 15-20 minutes, skimming off any foam that rises to the surface. This simmering time allows the radish to become tender and infuses the broth with deep flavor.

Add the sliced mushrooms and green onions to the pot and simmer for 5-7 minutes until the mushrooms are tender and cooked through. The mushrooms will absorb the aromatic broth and release their umami-rich flavors into the soup.

Remove the pot from heat and stir in the soy sauce and fish sauce until fully combined. Season with ground black pepper and taste, adding salt as needed. I like to add the soy and fish sauce at the end rather than during cooking because it allows me to adjust the saltiness to my preference without the flavors becoming muted through prolonged simmering. Serve hot and enjoy the clean, savory broth.