Warm the olive oil in a large sauté pan over medium heat. Season the salmon with salt and transfer to the hot sauté pan, skin side down. Sear the salmon without moving it for 3 minutes to crisp the skin. Turn the salmon over and add the potatoes, spring onions and garlic to the pan. Cook until the salmon is lightly browned and the garlic is fragrant, about 2 minutes.
Add the chicken stock, scraping up any brown bits from the bottom of the pan. Whisk in the mustard and let simmer for 1 to 2 minutes. Whisk in the butter and parsley and season to taste with salt and pepper. Serve immediately.
Adapted from Chef Michael Symon, Lola and Lolita, Cleveland