Classic Chicken Salad Croissant Sandwich

Ingredients

• 3/4 lb chicken breast
• salt and pepper
• 1 cup chicken broth/stock
• 1 tbsp of butter, optional
• 1 lemon
• 2 sprigs of tarragon, optional
• 1/4 cup mayonnaise, plus more to taste
• 1 tbsp Dijon mustard, plus more to taste
• 1 tbsp minced fresh parsley leaves
• 1 tbsp minced fresh chives
• 1/4 cup finely diced red onion (about 1/4 medium onion)
• 1/3 cup finely diced celery (about 2 stalks)
• 1/4 tsp garlic powder
• 2 croissants
• 4 lettuce leaves, such as butter, romaine, or use a handful of spinach