Loin Of Lamb En Cro�te With Shallot/balsamic Vinegar Sauce

• 4 lamb loins
• 4 sheets puff pastry
• 2 bell peppers (red)
• 1 garlic clove
• 1 egg
• 475 ml beef stock
• 300 ml balsamic vinegar
• 230 gr feta cheese
• 220 gr butter
• 45 ml olive oil