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This is the most important step: make sure your mixing bowl is fat-free and clean. De-grease by using a little bit of lemon juice and a paper towel. The reason for this is that you won't be able to beat the egg whites in a greasy mixing bowl.
Pour two egg whites into the mixing bowl and whisk at medium speed. The protein is stiff enough when you can hold the mixing bowl upside down without the protein falling out of it.
Now turn the mixer up to the highest setting, gradually pour the sugar into the beaten egg whites. Don't dump it all at once. Then also add cornstarch and vinegar. Mix for about 6 to 7 minutes on the highest settings.Then stop the machine.
Take some of the mixture between your thumb and forefinger and rub. It's done when it feels velvety and it looks kind of glossy. Pre-heat the oven to 110 degrees Celsius or 230 degrees Fahrenheit.
Add the egg whites to a piping-bag without nozzle and create rounds on the parchment paper. Bake them in the oven for about an hour, open the oven door slightly and let the meringues dry out for another hour.
Beat 200 ml heavy cream along with powdered sugar and vanilla extract. Add to a piping-bag without nozzle. Then also beat the remaining 50 ml heavy cream. Add sweet chestnut paste to the 50 ml cream and also add it to a piping-bag without nozzle.
If you're not planning to serve the pastries immediately, it's best to wait to put the ingredients together. Otherwise the meringues will become soft, so keep them in an air tight container until you're ready to serve them.
Add a layer of vanilla cream onto the meringue, you can use a spatula to coat it some more but that's optionally. Finish with chestnut paste, to do this you cut a small tip off the piping-bag and make circles on top of the cream so it looks like a mountain (mont in French).
Right before serving you add a bit of powdered sugar on top so it looks like there's snow on top (blanc). Enjoy!