Chunky beef and onion pie

Ingredients

• 1 kg chuck casserole beef, diced into cubes
• 2 tbsp plain flour
• 2-3 garlic cloves, crushed
• 1 large brown onion, finely chopped
• 2-3 celery stalks, finely chopped
• 1 large carrot, sliced
• 250 g brown mushrooms, sliced
• 2 cups cups beef stock
• 1 tbsp tomato paste
• 3 sprigs rosemary
• 3 bay leaves
• 1 ½ puff pastry sheets
• 1 egg yolk, lightly beaten
• Salt
• pepper