Prepare the sauce by combining tomato juice, Worcestershire sauce, dried mustard, brown sugar, vinegar, salt, bay leaf, and butter in a medium-sized saucepan.

Add quartered onion to the saucepan.

Bring the sauce to a boil, then reduce heat and simmer for 1.5 to 2 hours.

Strain the sauce through a sieve into a smaller pan to remove the bay leaf and onion.

Keep the sauce warm.

Spread mayonnaise on bread slices.

Add cooked chicken to the bread.

Pour some sauce over the chicken.

Top with another slice of bread.

Pour additional sauce on top of the sandwich.

Serve with small green peas and French fries.