• Gather all the ingredients.
  
• Cut ½ lb thinly sliced beef (chuck or ribeye) into 2-inch (5 cm) sections.
  
• Crush 2 cloves garlic (I use a garlic press). Slice 1 bunch komatsuna crosswise into 2-inch (5 cm) pieces. Separate the thick stems and leafy greens into different piles.
  
• Open 1 package maitake mushrooms and cut off the root end. Then, separate them into smaller clusters with your hands. I like to cut the maitake bunch in half with a knife before I break them into small chunks.
  

To Cook the Vegetables

• Preheat a wok, frying pan, or saucepan (I used a 10¼" carbon steel pan) over medium heat. When it's hot, add 1 Tbsp neutral oil. When the oil is hot, add the komatsuna stems and sauté to coat with oil.
  
• Add the maitake mushrooms. Toss to combine and coat with oil. Sauté until they develop a bit of color and become tender, with no stiffness and the center just cooked through—avoid overcooking so they retain their shape.
  
• When the mushrooms are almost done, add the komatsuna leaves. Season with ⅛ tsp kosher salt and ⅛ tsp freshly ground black pepper and toss it all together. Reserve the remaining salt and pepper to season the beef.
  
• When the leafy greens are wilted, transfer everything to a serving plate. Clean any remaining food particles from the pan with a paper towel.
  

To Cook the Beef

• Add 1 Tbsp unsalted butter and the crushed garlic to the pan. Stir briefly to coat the garlic in the melted butter. Then, add the sliced beef.
  
• Season with the remaining ⅛ tsp kosher salt and ⅛ tsp ground black pepper. Separate the beef slices (I use cooking chopsticks) so all the pieces come in contact with the hot pan and cook evenly.
  
• Once the beef is no longer pink, add 4 Tbsp ponzu. Stir to combine well. When the sauce begins to bubble, turn off the heat.
  

To Serve

• Transfer the beef onto the sautéed vegetables and spoon the pan sauce on top. Sprinkle with ½ tsp toasted white sesame seeds (optional). Serve immediately.
  

To Store

• Keep the leftovers in an airtight container in the refrigerator for 3 days or freezer for up to a month.