1. For the Steak: Place the sirloin in a ziplock bag along with the chopped rosemary, garlic and olive oil and let sit in the refrigerator for 20 to 30 minutes.
2. Season the marinated on both sides with salt and pepper and cook on high heat on a grill.This should take 10-14 minutes on each side to achieve medium-rare in temperature.
3. For the onion rings: In a bowl mix together the flour and egg.
4. Add the buttermilk, Guinness beer, salt and pepper and combine. Let this chill in the refrigerator.
5. For the Butter: Whisk the butter until light and fluffy.
6. Add in lemon juice, lemon zest, chives, parsley, salt and pepper and mix together and set to the side.
7. Dip the onion rings into the prepared batter.
8. In a pan, heat canola oil on medium-high heat and fry the onion rings until they are golden brown.
9. Place the onion rings next to the steak and place 1 tablespoon of lemon butter on top of the steak and serve.