Flank steak with horseradish cream sauce

Name: Flank steak with horseradish cream sauce
Prep time: 10 min
Cook time: 4 h 35 min
Total time: 4 h 35 min
Yield: 4 portions
Ingredients: 1000 g beef flank; 1 sprig fresh rosemary; 2 garlic cloves; 50 g Worcestershire sauce; 50 g extra virgin olive oil; 1 tbsp French mustard; 1 tbsp dried oregano; ¼ tsp ground black pepper; 100 g mayonnaise; 100 g crème fraîche; 20 g freshly squeezed lemon juice; 30 g horseradish cream; 1 tsp French mustard; 2 pinches cayenne pepper; 2 pinches sea salt