01 - Preheat oven to 375°F. Toss bread cubes with olive oil, garlic powder, dried thyme, and a pinch of salt until evenly coated. Spread in a single layer on a baking sheet and toast for 12-15 minutes, tossing halfway through, until golden brown and crisp. Remove from oven and set aside.
02 - In a large soup pot, melt butter over medium heat. Add diced onion and celery; cook for 5 minutes, stirring occasionally, until softened and translucent. Stir in minced garlic and cook for 1 minute more until fragrant, being careful not to brown the garlic.
03 - Add chopped broccoli (including stems) and diced potato to the pot. Cook for 2-3 minutes, stirring frequently. Season with 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1/4 teaspoon ground nutmeg, stirring to distribute evenly.
04 - Pour in vegetable broth and bring to a boil over high heat. Reduce heat to low, cover, and simmer for 15-20 minutes until vegetables are completely tender when pierced with a fork.
05 - Remove pot from heat. Using an immersion blender, purée soup directly in the pot until completely smooth and creamy. Alternatively, transfer soup in batches to a countertop blender and blend until smooth, returning each batch to the pot.
06 - Return pot to low heat. Stir in whole milk and shredded cheddar cheese; cook, stirring constantly, until cheese is completely melted and soup is heated through. Do not allow soup to boil. Taste and adjust seasoning with additional salt and pepper if needed.
07 - Ladle hot soup into bowls and top generously with homemade garlic-thyme croutons. Add an extra sprinkle of shredded cheddar cheese on top if desired. Serve immediately while hot.