Thoroughly wash the spinach under cold running water to remove all dirt and impurities. Pat dry with kitchen towels.

Bring a large pot of water to a boil. Add the spinach and blanch for 30 seconds. Immediately transfer to an ice bath to stop the cooking process.

Drain the blanched spinach using a strainer and gently squeeze out excess water. Be careful not to over-squeeze.

In a large mixing bowl, combine the spinach with garlic, sesame oil, soy sauce, and sesame seeds. Toss until the spinach is well-coated.

Season with additional soy sauce or sesame oil if needed. You can also add red pepper flakes for some heat.

Transfer the spinach banchan to a serving dish and sprinkle with additional sesame seeds if desired. Serve immediately as a side dish.

Place any leftover spinach banchan in an airtight container and refrigerate for up to 3 days. Reheat gently before serving.