Discard all but 2 tablespoons of the fat in the pot. Reduce the heat to medium. Add the onion, carrots and celery, cover and cook, stirring occasionally, until the vegetables are softened, about 20 minutes. Add the garlic and cook for 1 minute. Add the flour and cook, stirring occasionally, for 3 to 4 minutes. Add the ale and cook, stirring constantly, for 2 to 3 minutes. Add the Worcestershire, milk and broth, increase the heat to medium-high and bring to a simmer. Reduce the heat to medium-low and simmer for 10 to 12 minutes. Remove the pot from the heat and puree the soup with an immersion blender until smooth (or use a regular blender and do it in batches).