Brown mushrooms, remove, sear chicken (aggressively!) in same pan, cut into large pieces. Sauté bacon, onion and garlic, deglaze with Guinness, make roux, add stock, simmer with mushrooms to thicken (~10 min). Add chicken towards end. Pour into a baking dish, pipe on mashed potato, finish with butter and parmesan, bake 30 min.

Garlic butter mushrooms - Melt 1/4 of the butter in a large 30cm/12" non stick pan over high heat. Add mushrooms, toss for 3 - 4 minutes until you get some browning on the surface. Add another 1/4 of the butter, melt, toss to coat. Add 1/4 tsp each salt and pepper and half the garlic, toss 30 seconds until garlic is golden - mushrooms will still be hard inside, they finish cooking later. Remove into bowl (make sure you scrape out all garlic bits).

Sear chicken - Sprinkle the chicken with 1/2 tsp salt and 1/4 tsp pepper. In the same pan, melt another 1/4 of the butter until hot and foamy. Sear chicken 2 minutes on each side until nicely golden but inside is still raw (if they don't fit in a single layer, do in batches). Remove onto plate, once cool enough to handle cut into 2.5cm (1") pieces.

Bacon and onion - In the same pan, add bacon and stir for 15 seconds, then add the onion (there should be enough fat from the chicken). Cook for 2 minutes until the onion edges are golden and starting to soften. Add remaining garlic and stir 20 seconds.

Deglaze with Guinness - Add Guinness and let it simmer rapidly, scraping the base of the pan to loosen any golden bits into the liquid (“fond” = free flavour!), until the Guinness is reduced down by 75%.

Sauce - Lower heat to medium and add remaining butter. Once melted, sprinkle flour all across the surface and stir for 1 minute - it will look pasty. While stirring, pour in half the stock. Keep stirring until the flour paste dissolves into the stock, for lump-free sauce (yay!). Then add remaining stock, water, tomato paste, 1/4 tsp salt and 1/2 tsp pepper, stir well.

Simmer - Add the mushrooms plus all mushroom juices accumulated in the bowl into the pan. Simmer for 10 minutes or until the liquid reduces down into a fairly thick gravy and the mushrooms become soft. (Meanwhile, start the mash)

Thicken sauce - Add the chicken (plus all juices) and simmer for another 2 to 3 minutes until the gravy is quite thick and you can draw a path on the base of the pan. (Sauce thickness now = sauce thickness once baked). Taste - add more salt if needed (I don’t).

Assemble - Pour into a 1.5 - 2 L (6 - 8 cup) baking pan and smooth the surface. (Note 5 for other pan sizes)

Preheat oven to 200°C / 390°F (180°C fan-forced).

Duchess potato topping - Pipe mounds of mashed potato swirls on the surface. My swirls have a 4.5cm base (1.6"), about 4cm tall (1.4"), then I fill gaps with small swirls/blobs. I use all the mash! Drizzle with melted butter, sprinkle with parmesan. (Note 6 for no piping bag)

Bake for 30 minutes, rotating the pan at the 20 minute mark.

Serve - Rest for 10 minutes, sprinkle with parsley if using. Attack!

Make mash - Put the potatoes into a large pot of cold tap water. Bring to a boil over high heat then cook for 15 minutes until soft. Drain, pass through a potato ricer (smoother) or mash well with a potato masher in the now empty pot. Add butter, milk, 1/2 tsp salt and 1/8 tsp white pepper, stir through - it should be creamy but not loose (so it holds its form when piped).

Piping bag - Transfer mash into a piping bag fitted with a star tip. (Note 6 for no piping bag)