Ensure your griddle is preheated to high heat. This will allow the popcorn kernels to heat evenly and pop to perfection. Preheat until the grill is nice and hot.
Drizzle a generous amount of cooking oil onto the griddle surface, spreading it evenly to create a thin layer. The oil will help prevent the popcorn from sticking and ensure even heating.
Add the popcorn, cooking oil, melted butter, and salt into a small bowl, and mix well.
Spread a single layer of popcorn kernels on the griddle surface. Make sure the kernels are evenly distributed across the heated area. Place a large metal bowl, aluminum foil tent, or griddle cover over the popcorn kernels on the grill. This will create a contained space for the popcorn to pop while allowing steam to escape.
Pay close attention to the griddle's heat to prevent the popcorn from burning. Shake the griddle occasionally or lift the cover slightly to release steam and ensure even popping.
Once the popping slows down and there are a few seconds between pops, remove the griddle cover or foil tent, and turn off the heat. Drizzle melted butter over the popcorn for a rich buttery flavor. Sprinkle evenly over the popcorn with your desired seasonings, such as salt or spices. Toss gently to ensure all the kernels are coated.
Transfer the popcorn to a large bowl or individual serving containers. Dig in and savor the deliciousness of your Blackstone Griddle popcorn!