For the pie, heat a casserole or a large ovenproof pan over a high heat and add the oil. Once hot, add the steak pieces in batches and fry for 3-4 minutes, or until golden-brown on all sides, stirring regularly. Remove the cooked steak from the dish, transfer to a warm plate and set aside. Repeat the process with the remaining steak pieces, then set aside.
Add the onion, mushrooms, whole shallots and carrots to the emptied casserole and fry for 2-3 minutes, or until just softened.
Add the thyme, bay leaves and tomato purée and stir well to combine.
Add the ale and stir well, scraping any sediment up from the bottom of the casserole using a wooden spoon.
Return the browned steak pieces to the casserole, add the hot stock, stir well and bring the mixture to the boil. Turn down the heat, place a lid on the casserole and cook for 1½ hours, or until the beef is tender and the gravy has thickened.
Once cooked, remove the pie filling from the dish and set aside to cool.
Preheat the oven to 220C/425F/Gas 7.
Place the beef and gravy mixture in a 23cm diameter round ovenproof dish.
Roll out the pastry to 1cm/⅓in thickness and cut the pastry into a circle slightly bigger than the pie dish.
Brush a little water around the rim of the pie dish, then place the pastry over the filling and press the edges to seal the pastry to the dish.
Brush the pie with a little beaten egg, then place the pie in the oven and cook for 20-30 minutes, or until the pastry is pale golden-brown and has risen.
For the mushy peas, in a large bowl soak the peas in three times their volume of water and the bicarbonate of soda. Leave for at least four hours or, if you have the time, overnight.
Drain the peas, rinse under the tap, and place on the stove in a large pan and cover with water. Cover and bring to the boil. Once boiled, reduce the heat and simmer the peas for 1½-2 hours, stirring from time to time.
The peas should be soft and mushy in texture but not too dry. If they are wet, continue cooking over the heat with the lid off to dry out a little. Beat in the butter and season to taste with salt.
To serve, cut a slice of pie and place it on a plate and spoon some mushy peas on the side.