Roll out the puff pastry: mark the outline of the pot on the rolled pastry (1/2 cm thick) and cut about a centimetre outwards from the mark you made the with the pot. Flour generously and set aside.

Add the mushrooms and onion to a pot and cook until the mushrooms have shrunk. Add in tomato paste, flour, white wine, mustard and the stock cube.

Once everything is evenly coated, add in the chopped chicken and top up until everything is submerged with boiling water. This is the filling. You will want to reduce it enough so that it doesn't make the pastry soggy, but also so it's not dry.

Preheat the oven to 190C.

Add in the peas and salt and pepper to taste. Fill up each pot evenly and then place the pastry on top, wrapping it around the sides. Cut a small slit in the top. Brush on the beaten egg as an egg wash.

Cook for 30 minutes.

Meanwhile, parboil the potatoes for 5 minutes. Strain them once done and place on a chopping board. Salt thoroughly.

Cube the potatoes and add into a pan with 1 tbsp of the butter, which should be very hot.

Give it a mix a bit to stop burning, and, once it has gotten a bit crispy on all edges, add in the rest of the butter, garlic and rosemary. Baste the potatoes with the hot herby butter.

Take the pots out of the oven and place onto a plate. Add the sautéed potatoes and a dollop of mustard. Enjoy!