Pat salmon fillet dry with paper towels.
Season salmon fillet with salt and ground black pepper
Heat a large saute or frying pan over medium heat.
Add extra-virgin olive oil.
When oil is hot, add salmon fillet, skin side first.
Cook until brown and crispy, about 4-5 minutes.
Flip salmon fillet to cook the other side, cook for about 2-3 minutes or until salmon is cook through.
Transfer pan-seared salmon fillet on a serving platter, do not include the oil, set aside.
Using the same pan, make the sauce.
Add more olive oil if there's too little left on the pan.
Add garlic and saute until lightly browned and fragrant.
Add red chili pepper flakes, saute for a few seconds to release the heat then add broth or water, rum(if using) and lemon juice.
Let simmer until sauce is reduced to half.
Stir in butter and lemon zest and some parsley flakes, if using fresh parsley, add it at the end as garnish.
Drizzle the spicy lemon butter sauce all over the pan-seared salmon fillet.
Garnish as you like with more fresh parsley and lemon slices.
Serve immediately.
Enjoy it with steamed veggies or simple salad.