Melt butter in a large pot over medium heat. Add diced onion and cook for 3-4 minutes until softened and fragrant, stirring occasionally to prevent browning.
Stir in minced garlic and cook for 1 minute until the aroma fills your kitchen. The garlic should become light golden but never dark, as burnt garlic tastes bitter.
Add cubed sweet potatoes, carrots, and celery to the pot along with vegetable broth, dried thyme, and bay leaf. Bring to a rolling boil, then reduce heat and simmer for 15-18 minutes until all vegetables are completely tender when pierced with a fork.
Pour in the heavy cream while stirring gently to combine evenly throughout the creamy comforting sweet potato chowder recipe. Season with cayenne pepper, salt, and black pepper to taste, adjusting spice levels to your preference.
Remove the bay leaf and stir in fresh parsley just before serving. The soup thickens slightly as it cools, so serve immediately while it maintains that perfect creamy consistency.