2) Cut a slit and put a thin slice of butter inside each hamburger, making sure the butter is entirely encased within the meat.
3) Heat a grill, griddle, or frying pan and cook the hamburgers for 3 to 5 minutes on each side until done to taste. Remove to a plate and cover with aluminium foil.
4) Allow the hamburgers to rest for 5 minutes, then place each inside a bun. Serve immediately.