Heat a frying pan over medium heat.

Add the sausages and cook for 12-15 minutes, turning occasionally, until golden brown and cooked through.

Slice the bap in half and toast the cut sides until lightly browned.

Spread the butter on the cut sides of the bap.

Place the cooked sausages on the bottom half of the bap.

Drizzle ketchup over the sausages.

Place the top half of the bap on the sausages to create a sandwich.