1. Preheat your oven to 400°F.

2. Arrange the diced butternut squash, parsnips, sweet potatoes, carrots, and fennel slices on a baking sheet. Toss them with olive oil and salt, ensuring the vegetables are evenly coated. Roast for 25-30 minutes, stirring halfway, until tender and lightly caramelized.

3. While the vegetables are roasting, heat olive oil in a large soup pot over medium heat. Add diced onion and cook for 5-6 minutes until softened. Stir in all-purpose flour and cook for an additional minute.

4. Slowly whisk vegetable stock into the onion mixture. Add peeled and diced russet potatoes, roasted vegetables, and fresh thyme sprigs. Bring to a boil, then reduce heat and simmer for 20-25 minutes until potatoes are tender.

5. Remove thyme sprigs and use an immersion blender to puree the soup until smooth. Alternatively, transfer in batches to a traditional blender.

6. Stir in milk and season with additional salt and freshly ground black pepper to taste.

7. Ladle into bowls, garnishing with fresh thyme leaves and black pepper. Serve warm with crusty bread or crackers.