The ultimate makeover: Chicken pie

Name: The ultimate makeover: Chicken pie
Prep time: 30 min
Cook time: 45 min
Total time: 1 h 15 min
Cuisine: British
Ingredients: 450ml chicken stock, from a cube (I use Kallo, organic); 100ml white wine; 2 garlic cloves, finely chopped; 3 thyme sprigs; 1 tarragon sprig, plus 1 tbsp chopped tarragon leaves; 225g carrots, cut into batons; 4 skinless chicken breasts, 500g/1lb 2oz total weight; 225g leeks, sliced; 2 tbsp cornflour, mixed with 2 tbsp water; 3 tbsp crème fraîche; 1 heaped tsp Dijon mustard; 1 heaped tbsp chopped flat-leaf or curly parsley; 70g filo pastry (I used three 39 x 30cm sheets); 1 tbsp rapeseed oil