- Line metal loaf pan with plastic wrap, leaving plenty of wrap hanging over sides.
- Combine cream and instant espresso then whip to soft peaks. Reserve in refrigerator.
- Fill medium pan approximately ½ full of water and bring to simmer.
- Whisk together hazelnut liqueur, ⅓ cup sugar, and yolks in medium metal bowl. Scrap the seeds from vanilla bean into mixture and whisk to combine.
- Reduce heat to low and place bowl over pan. Make sure pan is not touching water. Whisk briskly until mixture lightens, thickens and reaches ribbon stage, around 3 to 4 minutes. (You will begin to see bottom of bowl while whisking and ribbon briefly forms on surface when some yolk mixture is drizzled over surface.)
- Remove bowl from pan and whisk until cool. Mixture should double in volume, mixer can be used. Reserve in refrigerator.
- Add egg whites and ½ cup sugar to medium metal bowl and place over same pan with water. Whisk until whites have warmed and sugar has dissolved, 3 to 4 minutes. Move mixture to stand mixer and whip until stiff peaks have formed and mixture has cooled.
- Gently fold egg yolk mixture into meringue then fold egg mixture into whipped cream.
- Pour semifreddo into prepared loaf pan. Wrap with plastic wrap and freeze for at least 8 hours.
- Toast pecans in oven until golden. Sprinkle to taste with Himalayan salt.
- Pour sugar into small sauce pan over low heat. Brush sides of pan with water to keep sugar from sticking to side.
- Once sugar comes to a boil increase heat to medium. When sugar turns golden brown, gently swirl pan to made uniform color then pour over pecans. Let cool. Sugar will be very hot. Take extreme care to not spill.
- Chill plates when ready to serve. Once semifreddo is frozen, remove from loaf pan and slice into ½-inch slices. Break croquant into small pieces and sprinkle onto semifreddo. Serve immediately.