Melt the butter over low heat, remove from the heat and cool for a minute or two.
Stir in the flour until smooth and return to a low flame stirring continuously for 3 mins.
Allow to cool for 5 mins; this is called the roux.
Bring the milk, bay leaf and thyme leaves to the boil slowly.
Remove the bay leaf, add the seasonings and whisk the roux off the heat.
Return to a medium heat and stir continuously until thickened and smooth.
Reduce the heat and cover with a piece of buttered greaseproof paper.
Cook very slowly for 10 mins.
Remove from the heat.
Remove the paper and whisk the sauce to be sure it is smooth and to release some of the heat.
Beat in the yolks, taste for seasoning but remember both the saltiness of the cheese as well as the volume of air added via the egg whites.
Beat the white until soft peaks emerge, add a little pinch of salt and continue to beat until stiff.
Beat a quarter of these whites into the sauce until smooth. Scatter the cheese over the remaining whites and then pour the sauce. Fold quickly and thoroughly.
Pour into previously buttered souffle dishes.
Place them in a baking dish, surround with boiling water and transfer to a preheated oven, about 180'C.
Bake for about 15mins until well risen.
Remove an allow to cool for 30mins before unmoulding.
The Second Cooking: choose either individual gratin dishes of an oven to table dish, which will accommodate them with some space to spare.
Unmould the souffles into the selected dishes, pour the cream over and around them finishing with the grated Gruyere cheese.
Bake in a preheated oven 160'C - 180'C until well risen and nicely coloured, about 10-15mins. Serve at once.
For 6 souffle dishes, each about 200ml capacity.
The souffles may be cooked initially up to two days in advance.