Add the butter, chopped garlic, diced carrot, onion and celery to the bowl of the Cook Processor fitted with the StirAssist. Season with pepper and salt.
Close the bowl of the Cook Processor and select BOIL P3. Press Start to activate the program. After Step 1, sprinkle the vegetables with the plain flour.
Close the bowl and press Start to activate Step 2. Let the flour bake for about 2 minutes to get rid of its floury taste. Then remove the center of the lid and slowly pour the warm whole milk into the bowl.
The mixture will start to thicken slowly. When all the milk is incorporated, gradually pour in the pale ale to the soup.
Close the center of the lid again and let the beer soup cook further.
After Step 2 add the strong mustard and the grated cheddar cheese to the bowl. Close the bowl again and press Start to activate Step 3.
Once the program is finished, press cancel to exit the keep warm mode. Check the seasoning of the beer cheese soup and add extra pepper, salt or mustard to taste if necessary. Divide the beer cheese soup over large bowls, sprinkle with the freshly chopped parsley and serve piping hot.