Heat the oil in a saucepan until almost smoking and add the corn so that it forms a layer 1–2 grains deep. Cover and shake the pan so that the corn becomes coated in the oil. Reduce the heat to medium and leave to cook for about 2 minutes while the corn is popping.
Shake the pan carefully once the popping subsides, then leave to cook for a further few seconds. Once the popping quietens down again, turn off the heat so that the popcorn doesn't burn.
Meanwhile, place the butter and spice mix in a small saucepan and heat over a low heat, stirring frequently, until melted.
Transfer the popcorn to a large bowl, drizzle over the spiced butter and stir until all the popcorn is coated in the butter. Serve immediately.