Put the oil in a frying pan and cook the onion until soft. Add the
carrot, celery and garlic and cook
until lightly browned. Mix in the
mince, breaking it up with a spoon.
Cook, stirring often, until the
meat is browned. Add the thyme,
tomatoes, stock, Worcestershire
sauce and parsley, and season
to taste. Cover tightly and simmer
for 15 minutes. Preheat the oven
to 200C/gas 6/fan 180C.
Sift the flour and baking powder
and rub in the butter. Add the
cheese and herbs, then the yogurt,
and mix to a soft dough. Turn out on
to a lightly floured board and knead
lightly. Roll to about 1cm/1⁄2in thick
and cut out 9 rounds.
Tip the mince mixture into an
ovenproof dish. Casually arrange
the dough circles on top of the
mince and brush with egg or milk.
Bake for about 20-25 minutes until
the topping is risen and golden
brown and the filling is bubbling.