1) Preheat the oven to 190C/375F/Gas 5.
2) Generously butter the sides and bottom of a 27cm flan tin.
3) Lay the pastry into the tin and trim to size.
4) Press the pastry well into the crease of the tin and prick the pastry base all over with a fork.
5) Line the tart case with baking paper and fill with baking beans. Blind bake for 15 minutes, then remove the beans and paper and return to the oven for a further 10 minutes.
6) Remove from the oven and set aside.
7) Meanwhile heat the butter in a large frying pan over a medium to low heat, add the onions, thyme, nutmeg and season with salt and pepper.
8) Cook for 10-15 minutes stirring regularly, making sure not to brown the onions.
9) To make the filling, beat the eggs with the cream and milk in a jug and season.
10) Spoon the onions into the base of the tart case and top with the egg mixture.
11) Cut the goats cheese into 8 slices and arrange round the top of the tart.
12) Bake in the preheated oven for 30-35 minutes, or until set and lightly browned on top.
13) Remove from the oven and leave to cool slightly before serving.