Heat a 12" skillet with 2 Tablespoons olive oil over medium-low heat. Add 1 chopped onion and cook until onion is softened, about 3-4 minutes. Add 2 cloves garlic and stir, cooking an additional 30 seconds.
2 Tablespoons olive oil, 1 medium yellow onion,, 2 cloves garlic,
Increase heat to Medium. Add about ⅓ of the cabbage. Stir to mix onions and garlic with the cabbage. Now leave it alone and let the cabbage start to brown, but be careful not to let it burn. Adjust the heat up or down as needed. Using a spatula, turn the cabbage over and let other side brown slightly. Season lightly with a dash of salt.
Add another ⅓ of the cabbage and 1 Tablespoon butter. Flip cabbage again after a couple minutes.
Finish with remaining cabbage and last tablespoon of butter. Once cabbage is browned to your liking, add more salt to taste and pepper, if desired. Remove from heat, season with red pepper flakes, if desired. Serve.