Put butter in a small saucepan and place on the griddle in a corner where it is not as hot.
Next, add oil to the grill and spread over griddle with a spatula.
Place the popcorn kernels on the griddle and spread into an even layer.
Cover popcorn kernels with a cooking dome and slide it around the cooking surface so the kernels roll around and don't burn. You need to keep moving the dome continuously to prevent burning.
After a minute or so you'll hear the corn kernels starting to pop. Do not lift dome, if you do the kernels will start popping all over the place.
Cook for about 3 to 4 minutes total, or until the kernels have all popped. You’ll know the popcorn is ready when the popping sound stops.
Use a spatula to carefully remove the popcorn and place in a bowl or tray. Pour the melted butter from the grill on top and season it with the salt.