On an ungreased baking sheet, toast almonds for 10 to 12 minutes, until light golden brown. Allow to cool.
Melt butter in a sauté pan over medium heat. Add almonds and salt and stir together until coated, about 4 minutes. Remove from heat.
In a bowl over a pot of slowly simmering water (or in the microwave at high heat stirring every 20 seconds), melt chocolate and set aside. Keep pot of water simmering on the stove – you’ll need it again!
Whip cream to soft peaks and store in fridge until ready to use.
Whisk together eggs, sugar, and extracts in a metal or glass bowl. Place bowl over simmering water and whisk constantly until doubled in volume, and whisk leaves a ribbon when lifted from bowl. Remove from heat. Whisk in melted chocolate and allow mixture to cool for about 10 minutes (so as to avoid melting whipped cream). Meanwhile, line a loaf pan with plastic wrap.
Fold whipped cream into chocolate mixture, in two additions, until evenly incorporated. Fold in toasted almonds and pour mixture into loaf pan. Freeze overnight.
Semifreddo can be spooned or scooped, but can also be unmolded and cut. To slice and plate, invert loaf pan onto a plate and remove pan and plastic wrap. Dust semifreddo with cocoa powder (turning on its sides to fully coat). Slice, wiping knife after every cut.