Preheat the oven to 375℉
Cut the cod filets into 1-inch cubes and place them in the bottom of a greased baking dish.
In a large cast iron skillet, melt the butter over medium heat.
Add the minced onions and garlic to the butter and sauté until soft.
Once the onions and garlic are soft, stir in the flour and cook for about 2 to 3 minutes.
Deglaze the pan with the pinot grigio, scraping the bottom of the pan to bring up any brown bits.
Simmer the wine for about 5 minutes or until it is reduced by half.
Add the milk, dry mustard, paprika, salt, and pepper to the skillet and stir to combine.
Remove the skillet from the heat and slowly whisk in the parmesan and cheddar cheese until smooth and creamy.
Pour the cheesy cream sauce over the cod pieces.
In a separate bowl, melt 1 tbsp of butter.
Stir in the bread crumbs until the bread crumbs are no longer dry.
Sprinkle the buttery bread crumbs over the top of the cod and cream sauce.
Bake for 15-20 minutes. The internal temperature of the center of the baking dish should be over 145℉.
Allow the dish to cool for 15 minutes before serving.