Bring a large pot of water to a boil. Add 1/2 teaspoon salt and the green beans. Blanch for 3-4 minutes until the beans turn bright green and tender-crisp. Drain and rinse with cold water to stop cooking.
Heat olive oil and butter in a large skillet over medium-high heat.
Add the minced garlic to the skillet and cook for about 30 seconds until lightly golden. Add the blanched green beans, then season with kosher salt and ground black pepper.
Toss and cook for 2-3 minutes until heated through. If using, sprinkle with red pepper flakes before serving.