Place a large pot over medium heat.
Add 1 tbsp butter to the pot and allow it to melt.
Add the chopped celery, diced carrots, and chopped onion.
Sauté the vegetables until softened, stirring occasionally.
Add the chicken broth, cubed red potatoes, dried thyme, bay leaf, and dried oregano to the pot.
Season with salt and pepper to taste.
Stir to combine the ingredients evenly.
Bring the mixture to a boil.
Once boiling, reduce the heat to medium-low.
Cover the pot and simmer for approximately 15 minutes, or until the potatoes are tender.
Add the corn and diced cooked ham to the pot.
Stir to combine.
Simmer for an additional 5 minutes, or until the corn and ham are heated through.
In a separate pot, melt the remaining 4 tbsp butter over medium heat.
Add the all-purpose flour to the melted butter.
Stir until the flour and butter are fully combined and a smooth paste forms.
Gradually whisk the milk into the flour mixture.
Continue whisking and cooking until the mixture thickens.
Remove the thickened milk mixture from the heat.
Stir in the sour cream or heavy whipping cream until smooth.
Pour the milk mixture into the soup pot.
Stir until the creamy mixture is fully incorporated into the chowder.
Heat gently until the chowder is warmed through. Do not boil after adding the dairy mixture.
Remove and discard the bay leaf.
Ladle the chowder into serving bowls.
Garnish with crumbled bacon and chopped green onions.
Serve warm.