To make the gratin, peel and slice the
potatoes no thicker than a 50p piece
using a mandolin, if you have one. Bring
the milk, cream, garlic, herbs and some
seasoning to the boil in a large saucepan,
then turn down the heat and simmer
for a few mins.
Slip the potatoes into the hot milk
mixture and simmer for 10 mins until
just cooked. Drain the potatoes in a
colander over a bowl to catch the liquid
– reserve the milk. While the potatoes are
simmering, heat half the butter in a frying
pan until foaming. Fry the mushrooms for
2 mins until just wilted, season with salt
and pepper and set aside.
Rub 2 small gratin dishes (or 1 medium)
with the remaining butter, sprinkle over
the thyme leaves and grate over some
of the cheese. Fill the dishes halfway
with potato slices, moisten with a little
milk and grate over more cheese. Fill
up the dishes with potato slices, add
enough milk to cover, then top with the
mushrooms and the rest of the cheese.
For the chicken, mix about two-thirds
of the butter with the lemon zest and half
the juice, the parsley, paprika and some
salt and pepper. Lift the skin slightly away
from each breast, spread or pipe the
flavoured butter under the skin, then
stretch the skin back over. Chill up to
a day in advance, if you like.
Heat oven to 220C/200C fan/gas 7.
Heat the remaining butter in an
ovenproof frying pan until foaming.
Pan-fry the chicken, basting constantly
with the butter until starting to brown.
Add the shallot, garlic, thyme and
stock. Place the chicken, skin-side up
in its pan, on the higher shelf of the oven,
and the gratins on the lower shelf. Roast
both for 25-30 mins, then remove the
chicken and rest for 15 mins, while the
gratins continue to cook.
To finish, remove the chicken from
the pan. Place the pan back on the heat,
squeeze over the remaining lemon juice
and bring everything to a hard boil. Pass
the sauce through a sieve, pressing down
firmly on all the soft shallot and garlic.
Heat a drizzle of olive oil in another
frying pan and reheat the leeks until they
start to colour. With the gratins cooked,
you are now ready to plate up.
Line six leeks up in a row in the
middle of each plate. Carve the chicken on a slant
into five thick slices. Neatly fan out each chicken
breast over the leeks. Spoon the sauce over the
chicken and around the leeks,
and serve with the potato gratin.