Simmer vinegar, bay leaf, spices, and sugar in a pan.
Add remaining ketchup ingredients and bring to a boil while stirring.
Simmer for 30 minutes, stirring frequently to prevent burning.
Blend the mixture in a food processor and strain through a sieve.
Thicken with cornflour paste if the sauce is too thin once cold.
Heat a deep fat fryer to 170°C.
Fry potatoes for 2-3 minutes until tender but not colored.
Drain potatoes and increase fryer temperature to 190°C.
Mix yeast and sugar in a bowl.
Whisk in beer, vinegar, flour, and salt.
Leave the batter to ferment until bubbles appear.
Dip cod fillets in batter and fry for 3-4 minutes until golden.
Remove fish with a slotted spoon and drain on paper.
Keep fish warm in the oven if necessary.
Fry chips again for 2-3 minutes until golden-brown and crisp.
Serve the cod with chips and the homemade ketchup.