Preheat your oven to 400F.
Place cod in a pyrex, ceramic baking dish or foil/parchment paper lined baking sheet. Lightly season both sides of the cod with salt and fresh ground pepper. Leave the cod on the countertop while preparing your sauce.
In a small sauce pan, on medium-low heat start to melt your butter. When it starts to melt add your olive oil.
Once the butter is fully melted, whisk in flour. Whisk until it starts to bubble.
Add lemon juice, zest, salt, dill and garlic powder to the butter flour mixture, Whisk briefly until all incorporated.
Place smashed garlic segments dispersed evenly on cod. I like to press it into the fish, so it's slightly embedded within the fish. This will help protect it from burning and also flavor the fish.
Pour and then lightly press the sauce onto the cod until evenly coated.
Cook in the oven for about 12-15 minutes, depending on the thickness, and then broil on high for 2 minutes. You know it's done when the fish easily flakes with slight pressure from a fork, and the garlic pieces are just slightly charred.