If not pre-sliced, cut the Swiss cheese into slices.
Toast the buns in a hot frying pan for 15 to 30 seconds with a dab of butter or drizzle of olive oil.
Add the burger patties and cook for 2 minutes on one side.
Flip and add a slice of cheese. Cook, covered, for 2 more minutes.
To make the sauce, mix the ketchup and mayo.
Optional: Add some whisky or cognac to the sauce for an extra kick!
Place the burger on the bun with the sauce. Add the tomatoes and parsley and top with the other half of the bun. Enjoy!
Average estimated amount for one serving