In the bowl of an electric mixer with the paddle attachment, beat the butter and confectioners' sugar until soft, about 2 minutes. Beat in the egg. In a medium bowl, whisk together the flour, almond flour, hazelnuts, and salt. Add the flour mixture to the butter mixture in two batches, scraping down the sides of the bowl in between additions. Mix until the dough is well combined. Scrape the dough onto a piece of plastic wrap and form it into a disk. Chill for at least 1 hour, until firm.
Preheat oven to 325 degrees F. Roll out the dough into a 12-inch round and fit into a 10-inch tart pan with a removable bottom. Trim excess dough. Use a fork to prick the crust all over to prevent air bubbles from forming. Bake the tart crust until it's pale golden all over, about 20 to 25 minutes. Transfer tart to a wire rack to cool. (Tart shell can be made 8 hours ahead.)
Triple Creme Filling: In a heavy-bottomed saucepan combine 3/4 cup of the milk and 3 tablespoons of the sugar, and bring the mixture to a simmer. Meanwhile, in a large bowl whisk together the remaining 1/4-cup milk, egg yolks, cornstarch and another 2 tablespoons of the sugar. Remove the milk mixture from the heat and add a little bit of it to the egg yolk mixture to warm it, whisking constantly to keep the yolks from cooking. Pour the egg yolk mixture into the hot milk mixture, whisking the milk constantly as you pour.
Return the custard to the stove and cook it over medium heat, whisking constantly until the consistency of pudding (pastry cream). Add the cheese and freshly grated nutmeg, and whisk until smooth. Strain the custard through a sieve into a clean bowl. In a small heavy saucepan, stir and combine the remaining cup of sugar, light corn syrup and water. Cook over medium heat until it reaches (soft ball) 240 degrees F on a candy thermometer. Meanwhile, in the bowl of an electric mixer fitted with a whip attachment, whip whites until they are opaque and hold very soft peaks. When the sugar syrup is ready, drizzle it into the whites in a slow and steady stream on low speed. Once fully incorporated, increase the speed and whip until stiff, but still warm.
Whisk 1/3 of meringue into pastry cream to lighten. Fold in remaining 2/3 in 2 separate additions. Mound into prepared tart shell. Bake in a preheated 350 degree oven for approximately 30 minutes or until tart is golden brown and springy to the touch.