Stir salt and flour together in a shallow dish. Dredge fish in flour mixture and shake off excess.
Melt 2 tablespoons of the butter with the 3 tablespoons of olive oil in a skillet. When butter and oil start to sizzle, add fish and cook for 3 minutes on each side. Remove and transfer to a plate.
For piccata sauce: Add the lemon juice, broth and capers to the same pan. Bring to boil, scraping up brown bits from the pan for extra flavor. Add remaining 2 tablespoons of butter to sauce and whisk vigorously. Simmer for 4 minutes.
Pour sauce over fish and garnish with parsley.
How do I know when my cod is done?We'll cook our fish on a medium-high heat, quick and fast. It goes from almost done to perfectly cooked very quickly. (If it begins to ooze, it's cooked through and should be removed from the heat immediately.)Here's a doneness test: when you see the fish begin to look opaque, slide a pairing knife through one of the seams in the flesh and pry it back to see if it's lost its transparency.There should still be some juice, but it will be mostly opaque and flake. The fish will continue to cook even after it’s removed from the heat. By the time you're ready to serve your cod it will be cooked through and ready for your piccata sauce.