
Melt the butter in a large pot over medium-high heat. Add the garlic and onion and cook for about 2 minutes, stirring often, until fragrant. Add the carrots and celery and cook for 2 more minutes, then stir in the red bell pepper and cook for 1 minute.
Sprinkle the flour over the vegetables and stir well so everything is evenly coated. Cook for 1 minute to remove the raw flour taste.
Gradually pour in about half of the broth, stirring constantly until the flour dissolves into a smooth base. Add the remaining broth, milk, and water, then stir in the dried thyme, stock powder, and black pepper. Add the corn and peas and mix well.
Bring the soup to a gentle simmer, then reduce the heat to medium-low so the broth stays lightly bubbling.
Break the pasta into shorter pieces and add it to the pot. Simmer for about 10 minutes, stirring occasionally, until the pasta is tender and the soup has thickened slightly. Taste and adjust with salt and pepper as needed.
Ladle the hot soup into bowls and finish with fresh thyme leaves, if using. Serve immediately.