For the Hazelnut Pot de Crème:
4 large egg yolks
2 ½ tablespoons hazelnut paste
1 cup plus 3 tablespoons milk
3 tablespoons plus 1 teaspoon granulated sugar
1 teaspoon vanilla extract
For the Chocolate Mousse:
2 ¾ cups heavy cream
For the Candied Almonds:
1 cup granulated sugar
1 cup sliced almonds
¼ cup chocolate shavings, for garnish
Preheat the oven to 325°F.
To prepare the Hazelnut Pot de Crème: Mix the egg yolks and hazelnut paste in a small bowl. In a small saucepan, combine the milk and sugar and bring to a boil. Remove from the heat, and temper the egg mixture by slowly pouring in the milk mixture while whisking vigorously. Stir in the vanilla extract and then pass through a fine-mesh strainer into a small baking dish. Place the baking dish into a larger baking pan, about 10 inches by 13 inches, and pour hot water into the baking pan, until it reaches about 1 inch up the side of the small baking dish; be careful not to splash any of the hot water into the hazelnut mixture. Transfer to the oven and back until the hazelnut crème is set, about 30 to 35 minutes. Remove from the oven and let cool completely.
To prepare the Chocolate Mousse: Pour 2 ¼ cups of the cream into a mixing bowl and whisk to soft peaks. Put the bowl in the refrigerator. Place the egg yolks in the bowl of an electric mixer fitted with a whisk attachment; let them sit while you prepare the sugar syrup.
Pour 2 tablespoons of water into a small saucepan, add the sugar, and set over medium heat, stirring to dissolve the sugar. Bring to a boil and continue cooking until the mixture reaches 248°F on a candy thermometer. Start beating the egg yolks on medium speed and gradually add the sugar syrup. Continue beating until the mixture is thick and cool, about 4 minutes.
Place the chopped chocolate in a small bowl. Pour the remaining ½ cup of cream in a saucepan and bring to a boil. Carefully pour the hot cream over the chopped chocolate and, using a hand whisk, mix to a smooth consistency. Using a spatula, fold the egg yolk mixture into the chocolate mixture. Then fold in the refrigerated whipped cream mixture in 3 or 4 increments.
Preheat the oven to 350°F.
To prepare the Candied Almonds: Pour ½ cup water into a small saucepan, add the sugar and set over medium heat, stirring to dissolve the sugar. Bring to a boil and cook for 1 minute. Remove the pan from the heat, pour the simple syrup into a mixing bowl and let cool for 15 minutes. Add the almond slices to the syrup, stirring to ensure they are completely coated. Using a slotted spoon, remove the almonds from the syrup and transfer to a rimmed baking sheet lined with parchment paper. Bake in the oven, stirring the nuts every few minutes to ensure even color, until the nuts are golden brown, 6 to 8 minutes. Remove and let the almonds cool completely.
To assemble: Scoop a serving of hazelnut pot de crème into the bottom of a large martini glass. Fit a pastry bag with an 11mm (medium) round flat tip. Fill the bag with the chocolate mousse and squeeze a serving of mousse on top of the hazelnut pot de crème. Sprinkle a few candied almond sliced and chocolate shavings over the mousse and serve immediately.