Peppered beef fillet with truffle mayo recipe | Sainsbury`s Magazine

Ingredients

• 1kg piece of middle beef fillet
• 2kg Maris Piper potatoes, peeled and cut into 2cm cubes
• 300ml sunflower or vegetable oil, plus a splash for the beef
• 3 tbsp black peppercorns
• 1 x 80g bag watercress
• a squeeze of lemon juice
• 3 large egg yolks
• zest of 1 lemon, plus a little juice if needed
• 2 tsp Dijon mustard
• 1 tbsp white wine vinegar
• 1-2 tbsp truffle oil, to taste (we used L’Aquila Truffoil)