Instructions:
- Melt half the butter in a large Dutch oven over medium heat. Add onion and celery; cook until softened (about 5-7 minutes). Add minced garlic, thyme, and rosemary; cook for 1 minute until fragrant.
- Clear a small space in the centre of the pot. Add the remaining butter and let it melt. Whisk in the flour rapidly, cooking the mixture (roux) for 1-2 minutes until it smells slightly nutty.
- Gradually whisk in the warm stock until the mixture is smooth, ensuring no lumps form. Bring to a gentle simmer.
- Add the diced potatoes to the simmering liquid. Season well with salt and pepper. Continue to simmer gently, partially covered, until the potatoes are fork-tender (about 15-20 minutes).
- Use an immersion blender to blend about 1/3 of the soup until smooth, leaving plenty of potato chunks for texture. Alternatively, scoop out 2 cups of soup/potatoes, blend them, and return to the pot.
- Reduce heat to low (the soup must not boil now). Stir in the milk/half-and-half and the optional Worcestershire sauce.
- Remove the pot completely from the heat source. Add the grated Cheddar gradually, stirring constantly until it is fully melted and incorporated smoothly.
- Taste and adjust salt and pepper as needed. Let the soup sit, off the heat, for 5 minutes to allow the flavours to meld.
- Ladle into bowls and garnish generously with fresh chives and parsley before serving hot.