In a large cast iron skillet over medium-high heat, add the butter and let it melt. Season the salmon on all sides with blackened seasoning and salt. Once the butter is melted and beginning to foam, add the salmon in. Cook on one side for 4-5 minutes, or until the flesh has changed colors ⅔ of the way up the side of the salmon. Flip, and cook for 2-3 minutes on the other side. Remove the salmon from the pan, and let it rest.
To the pan, add in the garlic, red onion, bell pepper, and tomato. Sauté for 5 minutes, or until the garlic is aromatic, the onions are softening and the tomatoes are beginning to break down. Add the bone broth, and simmer for 2-3 minutes, or until slightly reduced. Turn off the heat, add in the heavy cream and stir gently to combine. Taste for seasoning. Add the Salmon back into the pan, and serve!