Smoked mackerel chowder with hedgehog garlic bread

Name: Smoked mackerel chowder with hedgehog garlic bread
Ingredients: 4 garlic cloves, crushed; 50g butter, plus a large knob for the chowder, softened; 1 small round loaf of bread; 1 tsp vegetable oil, for cooking; 4 celery sticks, finely chopped, plus a few leaves to serve; 1 onion, finely chopped; 3 tbsp plain flour; 600ml whole milk; 2 large potatoes, cut into cubes; 200g pack smoked peppered mackerel, flaked; 200g frozen sweetcorn