Beef Stroganoff

INGREDIENTS

• 3 Tbs. olive oil
• 1 1/2 lb. top sirloin, cut into thin strips about 1
• inch wide and 2 inches long
• Salt and freshly ground pepper, to taste
• 3 Tbs. unsalted butter
• 3 leeks, white and light green portions only,
• cleaned and finely chopped
• 1 lb. cremini mushrooms, brushed clean and
• sliced
• 1 Tbs. tomato paste
• 2 Tbs. all-purpose flour
• 2 1/4 cups beef stock
• 1/3 cup crème fraîche
• 2 tsp. Dijon mustard
• 2 tsp. fresh lemon juice
• Finely chopped fresh flat-leaf parsley for garnish