Cougette Souffle

1 preheat the oven to 180c/350f gas mark 4 and butter 6-7 ramekins.
2 puree the diced courgettes in a liquidiser. in a wide pan, melt butter and add the flour. cover the pan and cook for about a minute until it smells toasted. add the milk and the puree and cook on a low to medium heat for 15-20 minutes.
3 put the grated cheeses in a bowl,add the hot courgette mixture and whisk together. Leave to cool briefly, then add the egg yolks and whisk.
4 in a separate bowl, whisk the egg whites and cream of tartar to form soft peaks.lightly whisk a quarter of the egg whites into the courgette mix to loosen it, then fold in the remainder, taking care not to knock out the air whisked in earlier.
5 spoon the mixture into the ramekins, level the tops and run a knife around the inside edges.place in a oven-proof container filled with boiling water half way up the ramekins. put on the middle shelf of the oven and bake for 25-30 minutes, until risen and golden brown. serve immediately