To make the tarragon oil, chop the tarragon
leaves, then warm the groundnut oil in a small
pan. Add the tarragon, season with a pinch of salt,
then liquidise until smooth with a stick blender.
Set aside. Can be done up to 2 days ahead.
Cook the potatoes in boiling salted water for
20-25 mins. Cooking them a bit longer than usual
will give them a very soft, almost creamy texture.
Drain and halve the potatoes lengthways and
season with salt and pepper.
While the potatoes cook, arrange the tomatoes
on a baking tray, season, then drizzle liberally with
walnut oil. Put under a pre-heated grill and cook
for 6-8 mins until they start to colour and soften.
Set aside to be served at room temperature.
Add the sliced red onions to the cooked potatoes,
with the lime juice. Cover and keep warm. Heat
oven to 220c/fan 200c/gas 7.
Rinse the mushrooms briefly and pat dry. Sauté
in butter over a high heat, then season. Add the
mushrooms to the potatoes and red onions. Stir
the mustard into the cream, then lightly whip the
cream (see tip, opposite). Season and stir it
amongst the potatoes, onions and mushrooms,
then spoon over a large ovenproof platter. Lay
the strips of cheese, overlapping haphazardly, on
top. Can be done up to 1 hr ahead.
Now finish it in style. Bake until the cheese begins to melt and is tinged
to a light golden brown, about 10-12 mins.
Arrange the grilled tomatoes down either side of
the platter, scatter the broken walnuts (if using)
Over the tomatoes and drizzle with tarragon oil.
Serve the rest of the tarragon oil separately.