Vegetarian Pot Pie - Guiding Stars

Ingredients

• 1 Tbsp. unsalted butter
• 2 heads fennel, chopped
• ½ yellow onion, chopped
• 2 carrots, chopped
• 12 oz. button mushrooms, sliced
• 1 russet potato, peeled and diced
• ¼ cup flour
• 1 cup low-sodium mushroom broth
• 1 cup whole milk
• 1 cup frozen baby green peas
• ¼ cup thinly sliced fresh chives
• ¼ cup parsley
• 1 Tbsp. white vinegar
• 1 egg yolk
• 2 tsp. water
• 1 sheet store-bought puff pastry