Melt butter in a small stockpot over medium-low heat. Add onion, thyme bundle, and corn, and season with salt. Cook, stirring occasionally, until very soft but not browned, about 20 minutes.
Add stock and potatoes and bring to a boil. Reduce heat to medium and simmer, stirring occasionally, until potatoes are tender, 8 to 10 minutes. Remove and discard thyme. Puree one third of the mixture until smooth, using an immersion blender (use caution when blending hot liquids). Return to pot and stir in half and half. Cook until chowder is hot. Season with salt and pepper. Garnish with chives and hot sauce, if desired; serve immediately.