Preheat your oven to 350°F. Move the puff pastry from the freezer to the fridge to thaw. Peel and chop the onions, garlic, carrots and celery. Slice the mushrooms.

In a large ovenproof pot, warm 1 tablespoon of olive oil over low heat and cook the onions for about 10 minutes, until softened.

Turn the heat up and add the garlic, carrots, celery and mushrooms. Stir, then add the beef, Italian herbs, a pinch of salt and the black pepper.

Fry hard and fast for 3 to 4 minutes, then pour in the Guinness (or beef stock). Stir in the flour and add just enough water to cover.

Bring to a simmer, cover, and transfer to the oven for 90 minutes to 2 hours, stirring once halfway. You want falling-apart tender meat and a dark, thick gravy. If it is still liquidy, reduce it on the stovetop. A wet filling means a soggy bottom (and nobody wants that).

Stir half the cheddar through the hot filling, then let it cool for at least 20 to 30 minutes. Or refrigerate it and build the pie tomorrow, the timing is flexible as long as the filling is cooled. Turn the oven up to 375°F.

Unfold both pastry sheets on a floured surface. They'll be a little too small for your dish, so roll each one out to roughly a 12 inch square, pressing the fold creases together as you go. Rolling the pastry out is also necessary to make it thinner, which will help the bottom layer bake through better. Line your pie dish with the first sheet, letting it hang slightly over the edges. Chill the lined dish and the second sheet until the filling is ready.

Spoon in the cooled filling and scatter the remaining cheese on top. Brush the pastry rim with beaten egg, lay the second sheet over, and pinch the edges together all the way around to seal. Trim any excess, lightly score a criss-cross on top, and cut a small slit in the center for steam.

Brush the top with egg wash and bake on the very bottom rack for 45 to 60 minutes, until puffed and deeply golden. Rest 10 minutes before slicing. Serve with a lovely green salad, or buttery mashed potatoes with garlicky green beans.