Steak sandwich with caramelised onions

Ingredients

• Lurpak® Soft Unsalted
• 2 demi-baguettes (approx. 125g)
• 200 g lean steaks sirloin, bavette/flank
• 1 tbsp vegetable oil
• 1 large rosemary sprig
• 3 garlic cloves
• ½ green bell bell peppers, seeded and sliced into small chunks
• 1 small red onion, peeled and sliced
• 1 small white onion, peeled and sliced
• 50 g arugula leaves
• salt to taste
• freshly ground pepper to taste