For the custard:
5 egg yolks plus 2 whole eggs
1/2 cup granulated sugar
1/4 teaspoon salt
2 teaspoons pure vanilla extract
2 cups heavy whipping cream
1/3 cup powdered sugar
1/2 cup plain yogurt or sour cream
4 ounces semi sweet chocolate , melted
For the garnish:
4 ounces semi sweet chocolate
1/8 -1/4 cup heavy whipping cream
mini chocolate chips, optional
Prepare a double boiler by bringing some water to boil in a small saucepan. Reduce to a simmer. Place a heat proof bowl over the saucepan. Make sure that the water does not come in contact with the bowl.
Place the eggs, yolks, granulated sugar, and salt in the bowl. Beat with a hand held mixer about 5 minutes or until pale and thick. This can also be done with a whisk. It may take up to 10 minutes.
Remove from heat and whisk in vanilla extract. Set aside to cool.
In the bowl of a table top mixer with the whisk attachment, beat the heavy whipping cream with powdered sugar until it begins to thicken. Add yogurt or sour cream and continue to beat until thick and fluffy.
Combine 1/3 of the whipped cream into the egg custard mixture to lighten it up with a whisk.
fold in the remaining whipped cream until well combined. There shouldn't be any white streaks in the mixture. If needed, whisk it to smooth it out, but try not to overwork the mixture so that it does not deflate.
Line a loaf pan (9inch x 5 inch x 3 inch) with plastic wrap.
Pour half of the cream mixture in the loaf pan.
Place the melted chocolate in a plastic bag with the tip snipped off. Drizzle half of the chocolate over the cream.
Pour the remaining cream over the chocolate and swirl the remaining chocolate on top of the cream. Use a knife to create a swirl pattern. Let the knife go all the way through the pan down to the bottom so that the chocolate in the center gets distributed evenly. These chocolate swirls will become crunchy nits of chocolate once the ice cream is ready.
Place the loaf pan in the freezer and let it set overnight or at least 6 hours.
To create the garnish, combine the chocolate with the cream and melt either on top of a double boiler or in the microwave.
Whisk until smooth and shiny. If it is still too thick add some hot heavy cream to it and whisk.
Take the semifreddo ice cream out of the freezer and invert onto a platter. Discard the plastic wrap.
Drizzle the melted chocolate mixture over the ice cream and garnish with mini chocolate chips.
This tastes best slightly softened. It will soften when left out at room temperature about 10 minutes.
Slice and serve! Enjoy!