Duck confit burger - Good Food Middle East

Ingredients

• 1 tbsp olive oil
• 1 red onion, finely sliced
• 2 tbsp onion marmalade
• 500g pack duck leg confit
• 4 brioche burger buns
• 1 tbsp butter, at room temperature
• 1 tbsp Dijon mustard
• 80g bag rocket or frisée salad leaves