Preheat your oven to 375°F (190°C).
In a medium mixing bowl, whisk together the large eggs, egg whites, whole milk, sea salt, and black pepper until the mixture is uniform and airy.
Melt the butter in a 10-inch oven-safe non-stick skillet over medium heat.
Add the diced yellow onion, thinly sliced leeks, and shredded carrots to the skillet, sautéing for 5-6 minutes until the vegetables are softened and fragrant.
Stir in the minced garlic and chopped kimchi, cooking for another 2 minutes to allow the flavors to meld.
Pour the egg mixture over the sautéed vegetables, gently tilting the pan to ensure the eggs reach all the edges.
Transfer the skillet to the middle rack of the oven and bake for 12-15 minutes, or until the center is set and the top is lightly golden.
Remove from the oven and let the frittata rest for 5 minutes before slicing into wedges to serve.