Heat oven to 220C/200C fan/gas 7.
Remove the stalks from the mushrooms.
Heat half the oil in a large frying pan
and sizzle the mushrooms for 3-4 mins
on each side until golden and cooked
through – add a drop more oil if needed.
Lift the mushrooms out onto kitchen
paper to drain.
Place the same pan back on the heat
with the rest of the oil. Fry the garlic for
a moment, add the spinach to the pan,
then cook for 2-3 mins over a high heat
until completely wilted. Season with salt
and pepper, then tip the spinach into a
large sieve to drain thoroughly.
On a lightly floured surface scattered
with the thyme leaves, roll the pastry out
to the thickness of a £1 coin. Using a
saucer and a larger-size plate, cut out
4 circles about 5cm wider than the
mushrooms (for the bottoms) and 4
circles about 10cm wider (for the tops),
re-rolling the trimmings if you need to.
Place the 4 smaller circles on a baking
tray and top each with a quarter of the
spinach, making sure the pile of spinach
isn’t wider than the mushrooms. Top
the spinach with a slice of cheese, then
a mushroom, smooth-side up, and top
the mushroom with another slice of
cheese. Brush the border to each circle
with egg, then gently stretch the larger
circle over the mushroom, trying not
to trap any air, then press the edges
together with a fork. Trim the edges
with a knife if you want, then brush each
generously with egg. Bake for 40 mins
until golden, then leave to cool for a
few mins before serving.