Toast the Pistachios (Optional but Recommended)
If pistachios are raw, lightly toast them in a dry pan over medium-low heat for a few minutes until fragrant, then let cool.

Cook the Sugar Syrup
In a saucepan over medium heat, combine sugar, corn syrup (or alternative), and water. Stir until the sugar dissolves.
Without stirring further, bring the mixture to a boil until it reaches the hard-ball stage (about 250–260 °F / 120–125 °C), using a candy thermometer if available.

Whip Egg Whites
While syrup is cooking, beat the egg whites and salt in a stand mixer or using a hand mixer until stiff peaks form.

Combine Syrup and Egg Whites
Once the syrup hits the right temperature, carefully and slowly pour it into the whipped egg whites while mixing on medium-high speed.
Continue whipping until mixture becomes thick, glossy, and begins to cool a bit.

Fold in Pistachios (and Optional Add-Ins)
Gently fold the toasted pistachios (and any optional dried fruit or chocolate pieces) into the nougat mixture until evenly distributed.

Shape and Set
Line a loaf pan (or similar) with parchment paper. Pour the nougat mixture into the pan, and spread/pat down evenly with a lightly oiled spatula or parchment-covered hands.
If you like, top with a few whole pistachios for a decorative finish. Press lightly.

Cool & Slice
Let the nougat cool completely at room temperature until firm enough to slice. Use a sharp knife (oil the blade lightly to prevent sticking) to cut into bars or bite-sized pieces.