3 lbs (1.4 kg) potatoes, peeled and cut in half
6 oz (170 g) aged cheddar, grated, divided
½ cup (125 ml) whipping cream
3 tsp (15 ml) salt, divided, plus more for cooking potatoes
freshly ground black pepper, to taste
4 tbsp (60 ml) butter, divided, plus more for greasing dish
½ medium onion, finely diced
1 clove garlic, minced
3 tbsp (45 ml) all-purpose flour
2 cups (500 ml) milk
1 lb (450 g) cod or halibut, bones removed and cut into bite-sized pieces
½ lb (225 g) salmon, bones removed and cut into bite-sized pieces
½ lb (225 g) hot-smoked salmon, broken into bite-sized pieces
1 cup (250 ml) frozen peas
1 tsp (5 ml) finely chopped fresh chives
2 tsp (10 ml) finely chopped fresh parsley leaves