Torrone is a white, meringue-based nougat that is sweetened with a combination of sugar and honey.
While normal caramel should not be stirred as it cooks, the torrone sugar must be stirred as it begins to cook
Grease a 9-x-13-inch (23-x-32-cm) pan and line it with parchment paper so that the paper comes up the sides.
Whip the egg whites in a stand mixer fitted with the whip attachment with the salt until foamy and then gradually add ¼ cup (50 g) of sugar until the whites hold a soft peak when the beater is lifted.
In a large saucepot, bring the remaining 2 cups (400 g) of sugar and the honey to a boil over high heat while stirring constantly. Keep stirring and use a candy thermometer to gauge when the sugar reaches 280 °F (138 °C), at which point stop stirring (the sugar will no longer be at risk to boil over) and continue boiling until the sugar reaches 315 °F (157 °C) – this takes about 4 minutes from when it hits 280 °F/138 °C. Remove the pot from the heat and stir it until it cools to about 300 °F (149 °C), 1-2 minutes.
Turn on the mixer to high speed and carefully pour the hot sugar down the inside of the mixer (this avoids splatters) and continue to whip on high speed until the meringue thickens and cools enough that it can be touched, about 4 minutes. When you first add the sugar the meringue will inflate, but then collapse a little as it continues to whip.
Remove the bowl from the mixer and stir in the almonds, pistachios, zest and vanilla by hand. Work quickly to scoop and spread the torrone into the prepared pan, using hands dusted with cornstarch, press this evenly into the pan and let it cool completely (3 hours) before slicing.
To slice, tip the torrone onto a cutting board, peel away the parchment paper and dust the torrone liberally with cornstarch. Use an oiled knife (wiped with vegetable oil or cooking spray) to cut the torrone into bite size pieces.