Put a wok or frying pan over the
heat while you thickly slice the
mushrooms. Tip the butter into the
pan and when sizzling add the
mushrooms and cook over a high
heat, stirring occasionally until the
mushrooms are tender and juicy.
Meanwhile toast and lightly butter
the bread and put on 2 plates.
Stir the mustard and some salt
and pepper into the mushrooms
with 4 tbsp of the soured cream
and, when lightly mixed, pile the
mushrooms and their creamy
sauce on the toast. Spoon the last
of the soured cream on top, snip
over the chives and grind over
some black pepper.