In a large heatproof bowl, mix together egg yolks, erythritol, and stevia extract. In a medium-size sauce pan, bring some water to boil and reduce the heat until the water is simmering. Suspend the bowl with yolks over the water, making sure the bowl is not touching the water. Using an electric mixer, beat continuously for a couple of minutes until the mixture is pale and creamy.
Add cocoa powder, vodka, pinch of salt, and vanilla extract. Mix well, and make sure you scrape the sides of the bowl well. Let the mixture cool down (in the fridge if you wish) before you continue.
Using a stand electric mixer, whisk the chilled whipping cream until stiff peaks are formed (about 2 to 3 minutes on high). Do not over whip.
Gently fold about ⅓ of the whipped into the chocolate-yolk mixture. Next, transfer the chocolate-yolk-cream mixture into the bowl with whipped cream and gently fold in until the mixture smooths out and becomes soft and silky. Try not to deflate the mixture by over mixing. You want it to remain airy.
Transfer half of the chocolate ice cream to a container that can be sealed. Put half of the chocolate-hazelnut sauce onto the first layer and make swirls with a knife or a spoon. Add the rest of the ice cream on top and put the rest of the chocolate-hazelnut sauce on it. Make the swirls.
You can choose to use multiple smaller containers. I prefer this option. This way you can enjoy the ice cream in 2 - 3 hours, and after that, when it has gotten harder, it softens quicker.
Gently cover the ice cream with a small piece of plastic wrap or parchment paper (or both). Seal the top and freeze for at least 6 hours. If you want to enjoy the ice cream sooner, pack it into smaller containers and leave it in the freezer for 2 - 3 hours. In this time, it reaches just the right consistency but it is still smooth and creamy (at - 65 °F). Enjoy within two weeks!