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PRE-HEAT the oven to 180 degrees Celsius or 350 degrees Fahrenheit. ROAST the hazelnuts in the oven for about 10 minutes. Meanwhile, ADD 100 ml espresso and 30 grams of sugar to a small saucepan.
Let it simmer on low heat until it becomes a coffee syrup. Keep about 6 hazelnuts aside for garnish and PLACE the rest of the roasted hazelnuts in a food processor or blender to create fine hazelnut crumbs.
Turn down the oven to 100 degrees Celsius or 210 degrees Fahrenheit. For a perfectly round pie, you can draw 3 equal circles on parchment paper and place them on baking trays. DEGREASE the whisk and bowl of your stand mixer using a few drops of lemon juice and a paper kitchen towel.
Add the egg whites to the bowl and mix until they form soft peaks. Gradually ADD 400 grams of sugar and mix until the egg whites form stiff peaks. Use a silicone spatula to carefully add about 3/4th of the roasted hazelnut crumbs to the egg whites.
ADD the hazelnut egg whites to a piping-bag without a nozzle and fill the 3 circles equal to the whites. PLACE the 3 egg white rounds into the oven and bake them for at least 1 hour, depending on the oven and thickness of the egg white rounds.
They shouldn't be soft at all, so cooked all the way through.
Meanwhile prepare a home-made custard for the mocha cream later on. HEAT milk and vanilla on low heat. BEAT the egg yolks, 100-gram sugar, and 2 tablespoons of flour to a pale and fluffy texture.
Add a bit of the warm milk to the egg yolks while you keep on mixing to prevent it from creating any lumps. Then COMBINE all of the milk with the egg yolk mixture and let them cook some more on low heat.
Keep on stirring with a silicone spatula to prevent it from burning. The custard is done when you can draw a line on the spatula with your finger and the line stays visible. POUR the custard into a bowl and cover with parchment paper.
Let the custard, coffee syrup, and 3 large meringues cool off completely.
Use a stand mixer or electric mixer to create fluffy butter. ADD 100 gram powdered sugar, coffee syrup, and custard. When it's combined well, it's done!
SMEAR 1 meringue with a layer of mocha cream, then a second meringue, another layer of mocha cream, and the 3rd meringue on top. Finish the pie with mocha cream on top and also on the sides.
For garnishing the pie, you can also add some of the cream into a piping bag with a star nozzle.
DIVIDE nougatine nuts onto the sides of the pie and DIVIDE the rest of the roasted hazelnut crumbs on top. Finish the pie off with the whole roasted hazelnuts and a bit of cocoa powder. Enjoy!