Puff Pastry Palmiers

Ingredients (8)

• 2 sheets frozen puff pastry, thawed
• 1 large white onion
• 2 tablespoons unsalted butter
• 1 teaspoon brown sugar
• 1 teaspoon red wine vinegar
• Pinch of salt
• 4-6 ounces blue cheese, crumbled
• 1 egg + 1 Tbsp. water