Begin by peeling and cubing the potatoes. Aim for uniform pieces so they cook evenly. Next, finely chop the onion and celery. Slice the mushrooms thinly. The right preparation here allows everything to cook uniformly, presenting a lovely texture.

In a large pot, melt the unsalted butter over medium heat. Add in the diced onions and chopped celery. Sauté until the onion turns translucent—about 5-7 minutes. This step builds a strong flavor base for the chowder.

Once your onions and celery are looking good, toss in the sliced mushrooms. Stir them frequently, allowing them to release their moisture and absorb the savory butter. Cook for about another 3-4 minutes.

Sprinkle the flour over the mix and stir well to coat. This is your thickening agent! Gradually add in the homemade chicken stock and seafood broth or clam juice, stirring constantly to avoid lumps. Then, fold in the cubed potatoes.

Sprinkle in the Old Bay Seasoning, salt, and pepper. This blend lifts the dish and is essential for that traditional chowder taste. Let the flavors mingle as the mixture comes to a gentle boil.

Reduce to a simmer and maintain that gentle heat for about 15 minutes. Stir occasionally to ensure nothing sticks to the bottom. The potatoes should be fork-tender by the end of this step.

Once the potatoes are ready, incorporate the fresh cod and corn kernels. They need a shorter cooking time, roughly 5-7 minutes. At this point, keep an eye on it. You want the fish to be tender, not overcooked.

Finally, pour in the evaporated milk. This gives the chowder its signature creamy texture. Stir well and let it heat through without boiling. When ready to serve, ladle into bowls and sprinkle with crispy bacon bits and fresh parsley for garnish.