Melt butter in a large pot over medium heat. Add diced onion and minced garlic, sautéing for 3-4 minutes until softened and fragrant.
Stir in diced potatoes, red bell pepper, dried thyme, salt, and black pepper, cooking for 2 minutes to coat everything in the butter mixture and release aromatic flavors.
Pour in chicken broth and bring the mixture to a boil over medium-high heat for about 5 minutes, then reduce heat to medium and simmer gently.
Add corn kernels and simmer this creamy comforting corn chowder recipe for 10-12 minutes until potatoes are tender and the broth is infused with sweet corn flavor.
In a small bowl, whisk cornstarch with water to create a smooth slurry, then stir it into the simmering chowder to thicken over 2 minutes of gentle stirring.
Reduce heat to low and stir in heavy cream, then add shredded cheddar cheese while stirring constantly for 1-2 minutes until completely melted and incorporated throughout.
Taste and adjust seasoning as needed, then ladle the comfort soup into bowls and garnish generously with sliced green onions for fresh color and mild onion bite.