Caramelized Tarts - Pennant Bakery

Ingredients

• 1 large egg
• 1 tbsp. milk
• 4 cups thinly sliced sweet onion, roughly 2 large onions
• 2 tbsp. vegetable oil or olive oil
• 2 tbsp. butter
• 1 tsp. vegetable broth paste
• 1 tbsp. sugar
• 1 tbsp. white balsamic
• 1 – 10”x15” Sheet Pennant frozen Puff Pastry sheet*
• 1 tbsp. + ¾ tsp. Dijon mustard
• ¾ cup gruyere cheese