Mix together all of the Spice Rub ingredients in a medium bowl. Pat mahi mahi dry and rub spices into the fish.
Melt 1 tablespoon butter in 2 tablespoons olive oil over medium-high heat in a large heavy bottom skillet. Once hot, add fillets, turn heat down to medium and cook approximately 4 minutes, flip fillets over, then cook an addition 2-4 minutes to your liking (it will depend on thickness,; mahi-mahi should reach an internal temperature of 137°F). If fish is browning too quickly, then turn down the heat. Remove mahi mahi to a plate and tent with foil.
If needed, drain oil from skillet so you are left with about 1 tablespoon oil. Add shallot and sauté while scraping up the drippings for 2 minutes or until softened. Add garlic and sauté 30 seconds.
Whisk chicken broth with cornstarch and add to skillet along with heavy cream, lemon juice, thyme and parsley. Simmer until reduced by half and slightly thickened, about 4-5 minutes. Season with salt and pepper to taste (I use about ¼ teaspoon each) and add additional lemon juice if desired.
Nestle mahi mahi fillets back into the skillet and spoon sauce over the fillets. Garnish with fresh chives and/or parsley (optional). Serve immediately with rice, mashed potatoes or pasta.