Flank steak with horseradish cream sauce

Mustard marinade

• 1000 g beef flank, sinew removed (see Tips)
• 1 sprig fresh rosemary, leaves only
• 2 garlic cloves
• 50 g Worcestershire sauce
• 50 g extra virgin olive oil, plus extra to grease
• 1 tbsp French mustard
• 1 tbsp dried oregano
• ¼ tsp ground black pepper

Horseradish cream sauce

• 100 g mayonnaise (see Tips)
• 100 g crème fraîche (see Tips)
• 20 g freshly squeezed lemon juice
• 30 g horseradish cream
• 1 tsp French mustard
• 2 pinches cayenne pepper
• 2 pinches sea salt