- Preheat the oven to 150ºC/gas 2. Cover a baking tray with greaseproof paper.
- Pour the oil into a large, heavy-based pan over a medium-high heat.
- Once hot, add the corn and shake the pan gently so the kernels are in one layer and coated in oil.
- Cover with a lid and leave over the heat, shaking the pan gently every 30 seconds. The popcorn is ready when the pops are about 2 to 3 seconds apart. Tip into a large bowl.
- Melt the butter in a small pan over a low heat and stir in the Marmite until you have a smooth, glossy liquid. Pour the Marmite mixture over the popcorn and stir well until every piece is coated.
- Spread the popcorn over the lined baking tray and place in the oven for 3 to 4 minutes to crisp up a little.