Add all the marinade ingredients to a bowl and whisk to combine.
¾ cup beef stock, 3 Tbsp. rice wine vinegar, 1 thumb-size ginger, 1 garlic clove, Sea salt and freshly ground black pepper
Add the steak to the marinade, gently toss to combine, and refrigerate for at least 15 minutes.
1 lb. thinly sliced flank steak or sirloin
Heat some cooking fat in a large sauté pan placed over medium-high heat.
Cooking fat
Remove the steak from the marinade, reserving the marinade.
Add the steak and the garlic to the pan and sauté for 3 to 4 minutes.
2 garlic cloves
Remove the steak and set aside.
Add the mushrooms, kale, and reserved marinade, and cook for another 3 to 4 minutes.
8 oz. cremini mushrooms, 3 cups rapini, 4 oz. shiitake mushrooms
Return the steak to the skillet and stir to combine.
Serve immediately.