Annas Caramelised onion and leek tart filling

filling:
60 g butter
3 leeks, white part only, sliced
400g onions, halved, sliced
1 tablespoon brown sugar
1 1/4 cups pouring cream
1 tablesppon thyme leaves
3 eggs lightly beaten
150g gruyere cheese, finely chopped

melt butter in pan, add onions and leeks and cook over low heat 20 mins
add brown sugar and thyme, increase heat and cook another 5-10 min, don't burn.
when its nice and soft, remove from heat and allow to cool.
combine cream, beaten eggs, cheese and onion mix. mix well and season. pour into preparted pastry cases (? try mini) and cook 200C for 30-40 mins untill golden brown