Step 1

Preheat the oven to 160°C/°F/Gas Mark 3.

Step 2

Add the beef to a hot, deep casserole dish with a dash of oil and sprinkle over the flour. Give the meat a good stir until the flour disappears from sight and the meat is very well-browned.

Step 3

Add the remaining ingredients needed for the filling; the mushrooms, garlic, onions, carrots, celery, ale, beef stock, thyme and mustard. Again, give everything a good stir so they are evenly distributed and season well.

Step 4

Pop the lid on and place the dish in the preheated oven for 3 hours, occasionally stirring to make sure the bottom isn’t catching, or adding a little water if you think the mixture is becoming dry.

Step 5

While the stew is cooking, make your mash. Simply empty the celeriac and potato into a large saucepan and fill with cold water.

Step 6

Bring to the boil and simmer for 15–20 minutes, until the vegetables are completely tender. Drain and mash, stirring in the milk and knob of butter. Season to taste.

Step 7

Remove the casserole dish from the oven and allow your pie filling to cool. Transfer to a 1.5 litre, ovenproof dish.

Step 8

Preheat the oven to 180°C/350°F/Gas Mark 4.

Step 9

Bake for 30 minutes until the top is crusty and golden brown and the filling is bubbling below. Garnish with a little fresh thyme before serving