Step 1: Grab a Dutch oven or heavy-bottomed soup pot. Place it over medium heat and melt the 2 tablespoons of butter until shimmering and golden.
Step 2: Add the diced yellow onion to the melted butter. Stir gently and cook for about 5 minutes, until softened and translucent, building a sweet flavor base.
Step 3: Stir in the minced garlic and cook for just 60 seconds until aromatic, being careful not to let it brown to avoid bitterness.
Step 4: Add the dried rosemary, thyme, oregano, celery salt, a pinch of regular salt, freshly ground black pepper, and optionally, a dash of cayenne pepper. Stir in the chopped zucchini. Cook this aromatic mix for about 5 minutes, stirring occasionally, until the zucchini begins to soften slightly.
Step 5: Add the diced potatoes, chicken broth, and soy sauce to the pot. Stir everything well to combine all the flavors.
Step 6: Bring the soup to a gentle boil over medium-high heat. As soon as it starts bubbling, immediately reduce the heat to medium to maintain a steady simmer.
Step 7: Partially cover the pot and let it simmer for about 15-20 minutes, or until the potatoes and zucchini are fork-tender and the flavors have melded together.
Step 8: Carefully remove the pot from the heat. Using an immersion blender, carefully puree the soup directly in the pot until it is wonderfully smooth and creamy. If using a regular blender, transfer batches carefully, filling only halfway, and leaving the vent open (covered with a kitchen towel) to allow steam to escape.
Step 9: Once the soup is beautifully smooth, stir in the room temperature heavy cream and shredded cheddar cheese. Continue stirring until both are completely melted and evenly combined, creating a luxurious, rich texture.
Step 10: Ladle the creamy soup into bowls. Serve warm, optionally garnished with fresh herbs or accompanied by a crusty piece of bread. Enjoy!