Cubano sandwich with rum onions

Ingredients:

• 2 onions, sliced 
• Knob butter 
• Glug oil
• ¼ cup (60ml) rum (optional)
• 16 slices ciabatta
• ¼ cup (60ml) Dijon mustard
• 24 slices roast beef
• 16 slices emmental
• 4 gherkins, thinly sliced

Method:

1. Fry onion over a medium heat in melted butter and oil until softened. 
2. Increase heat and add rum, if using. 
3. Cook until evaporated. 
4. Smear half the bread with mustard. 
5. Top with beef, cheese, gherkins and fried onion. 
6. Sandwich together with remaining slices. 
7. Toast over an open fire or in a hot non-stick pan until cheese melts, turning frequently to prevent it from burning. 
8. Serve immediately.