If your hazelnuts aren't roasted and peeled:In a large pan, pour in the hazelnuts. Place over medium low heat, stirring frequently to keep from burning, until they become golden brown and the skins start to flake off.
Pour the toasted hazelnuts onto a kitchen towel and rub against each other with the towel to remove the skins. Ideally this will take off most of the skins, if it doesn't, use your fingers to peel as much as you can (but don't stress if there's still some left).
Transfer the toasted and peeled hazelnuts to a high powered blender or food processor. Blend on medium low speed, slowly increasing to high until a smooth butter forms - set aside.
In a small microwave safe bowl, add in the dark chocolate and microwave in 30 second increments, stirring in between until melted.
Separate the sweetened condensed milk into three separate mixing bowls. Add the espresso powder into one bowl and beat until dissolved and only a few small flecks remain.
In the bowl of a stand mixer or a large mixing bowl, add in the heavy cream, vanilla bean paste, and fine sea salt. Whip on medium high speed until stiff peaks form.
Add 1/3 of the whipped cream to each of the bowls with the sweetened condensed milk. Fold the whipped cream into the sweetened condensed milks until smooth. Be careful not to stir and knock all the air out.
Add the hazelnut butter into one of the two bowls without the espresso mixture and fold again to combine. Swirl in the chocolate hazelnut spread and only fold three times.
Pour the melted and cooled chocolate into the third bowl and use the mixer to beat until smooth. Sprinkle in the flaky salt and fold to combine.
Crumble the halva into the coffee bowl and fold once more.