Finely chop the onion and celery. Crush or finely chop the garlic. Finely chop the thyme leaves, discarding the tough stems. Heat 2 tsp olive oil and 20g butter in a medium saucepan over medium heat. Cook the onion, celery, garlic and thyme, stirring regularly, for 5 mins or until softened.
Step 2 — Prep ingredients
While the aromatics are cooking, quarter the carrot lengthwise and cut into 1cm chunks. Peel the potato and cut into 2cm chunks. Discard the husk and silks from the corn, then slice the kernels from the cob. Crumble 3 stock cubes* into a heatproof jug, add 625ml (2½ cups) boiling water and stir to dissolve.
Step 3 — Add stock
Add 1 tbs flour to the aromatics and cook, stirring, for 1 min. Gradually add the stock, stirring constantly to prevent lumps forming and bring to the boil.
Step 4 — Cook vegetables
Add the carrot, potato and corn to the soup and season with pepper. Cook over medium heat, stirring regularly, for 10 mins or until the vegetables are almost tender.
Step 5 — Cook fish
Add the fish to the soup. Reduce the heat to medium and cook, stirring occasionally, for 6 mins or until the fish is cooked through. Remove the fish with a slotted spoon. Stir 125ml (½ cup) milk into the soup, reduce the heat to low and cook for 1-2 mins until heated through.
Step 6 — Flake fish and serve
Meanwhile, remove the skin from the fish, then flake the fish into large chunks. Add the fish to the chowder. Divide the chowder among bowls to serve.