Melt the butter in a large pot over medium heat. Add the chopped onion and minced garlic and sauté for 3-4 minutes until the onion is translucent.
Add the flour to the pot and stir for 2-3 minutes until the mixture is well combined and slightly golden in color.
Slowly pour in the broth, stirring constantly to prevent any lumps from forming. Increase the heat to medium-high and bring the mixture to a boil.
Add the frozen corn, dried thyme, salt, and pepper to the pot. Reduce the heat to medium-low and let the mixture simmer for 10-15 minutes until the corn is tender.
Add the shrimp to the pot and cook for an additional 3-5 minutes until the shrimp are pink and opaque.
Finally, pour in the heavy cream and stir until the chowder is heated through.