Heat skillet over medium-high heat. Add butter to coat the pan. Place rice in skillet and smash down with a spatula so that a medium thin rice patty forms in half the pan. Drizzle kimchi brine on top of rice and let set till underside begins to brown and crisp up. Flip rice patty and repeat. Meanwhile, fry egg in same pan until desired doneness (alternatively you could poach or soft boil the egg). When rice patty is crispy, place in bowl and sprinkle with rice vinegar, add egg, kimchi, spinach, and peashoots (spinach can be sautéed or enjoyed raw).