Ingredients

• 3 tablespoons, unsalted butter
  
• 3 tablespoons, il Fustino Mission Extra Virgin Olive Oil
  
• 2 large, yellow onions - halved lengthwise and thinly sliced
  
• 1 sprig, fresh rosemary (Plus more for garnishing)
  
• 1/4 cup, milk
  
• 1 medium, egg
  
• 3/4 pound, prepared puff pastry
  
• 1 1/2 ounces, Stilton cheese - crumbled
  
• 2 tablespoons, pine nuts - toasted
  
• il Fustino 25 year old balsamic vinegar
  

Method

1. In a large flat bottomed skillet over low heat, melt butter and oil
   
2. Add onions and rosemary
   
3. Cook, tossing occasionally until onions are limp and golden brown, 30 to 40 minutes
   
4. Allow to cool
   
5. Preheat oven to 400 degrees
   
6. Line an 11" X 17" baking sheet with parchment paper
   
7. Unroll prepared puff pastry sheet and place on baking surface
   
8. Whisk egg until smooth, add milk and continue to whisk until blended
   
9. Stir in caramelized onion mixture
   
10. Leaving a one-inch border, use a fork to spread onion and egg mixture evenly over pastry (let excess egg mixture drip back into the bowl)
    
11. Scatter cheese and toasted pine nuts over onion and egg mixture
    
12. Use a pastry brush to dab edges of tart with leftover onion and egg mixture
    
13. Gently fold over edges of tart to form a lip and brush with more onion and egg mixture
    
14. Bake until pastry is puffed and golden, approximately 25 to 30 minutes
    
15. Cut into two to three inch squares and garnish with rosemary needles and il Fustino balsamic vinegar
    
16. Can be served warm or at room temperature