A long time ago I asked about Swiss Meringues on my other blog. I got a comment on it today (from "anonymous"), explaining how they are made. I reproduce it here.
The Gruyère Meringue is a oven-baked "Swiss Meringue"
Heat a bain-Marie at 50-55 Celsius (a tin pot plunged into a saucepan of hot water. The water must not boil)
Put 4 egg-whites in the pot. Add 250g of granulated sugar. Add a drop of lemon juice (to keep the eggs shining and white and to keep the meringue smooth)
Whip the egg-whites + sugar at medium speed then stiffly. When the meringue is cooked (snowy, shining, and sticking like melted marshmallows), take the pot out of the bain-Marie and let the swiss meringue cool down.
With a pastry bag, form balls of swiss meringue on a nonstick plate. Bake the meringue at 110-130 Celsius (Th 2-3) for 15 minutes in the case of small meringues (the larger the longer). When a hard crust has formed, stop the oven, and let the meringues cool down inside the oven. Note that the meringues must remain white, if they are turning golden, the oven is too hot.
As for the double cream, it is Chantilly made out of fresh double cream from Gruyère. The cows of Gruyère are famous for the taste of their milk since they graze the flowers covering the Alps mountain. There is no way you can find any equivalent in a supermarket. So buy some whipping cream (the real stuff, i.e. fluid cream without any additive). If you cannot find it, add 10cl of full milk into 30cl of sour cream (best to use triple cream, i.e. Mascarpone). Add some vanilla for the taste as well as a small quantity of icing sugar (50g for 30cl of cream). To get a perfect Chantilly, flush the cream through a seltzer (a spray with a special canister to make whipped cream). If you don't have the right tool, add some gelling agent to the cream (carob ideally), cool it down to a freezing temperature, then whisk it.
In Gruyère, they serve a sandwich made of two baked meringues with a thick layer of Chantilly in-between.
If I may add, this commentator is correct. I haven't had Gruyère cream, but the local milk I had in Switzerland was one of a kind--and very good.