Line an 8x8 inch square pan with parchment paper, leaving an overhang on two sides to help lift the nougat out. Place one sheet of wafer paper on the bottom of the lined pan.

Preheat oven to 300°F (150°C). Spread pistachios and almonds on a baking sheet. Toast for 5-7 minutes, until fragrant. Let cool completely. This enhances their flavor.

In a heavy-bottomed saucepan, combine water, granulated sugar, honey, and corn syrup. Stir gently over medium heat until sugar dissolves. Insert a candy thermometer, ensuring it doesn't touch the bottom of the pan. Bring the mixture to a boil without stirring.

While the sugar syrup is heating, in the bowl of a stand mixer fitted with the whisk attachment, add egg whites and cream of tartar. Beat on medium speed until soft peaks form.

Continue to cook the sugar syrup until it reaches 250°F (121°C) (soft ball stage). Once it reaches this temperature, immediately reduce mixer speed to low and slowly pour about half of this syrup into the egg whites in a steady stream. Increase speed to high and beat until stiff, glossy peaks form and the meringue is thick and stable.

Return the remaining sugar syrup to medium heat and continue cooking until it reaches 300°F (149°C) (hard ball stage). This can take an additional 5-10 minutes. Be very careful, this syrup is extremely hot.

With the mixer running on medium-high speed, slowly and carefully pour the remaining hot 300°F (149°C) syrup into the meringue in a thin, steady stream. Continue beating on high speed for 8-10 minutes until the mixture is very thick, glossy, and has cooled down significantly (the bowl should be warm but not hot to the touch). The nougat should be pulling away from the sides of the bowl.

Reduce mixer speed to low. Add vanilla extract and salt. Mix briefly. Add the toasted pistachios and almonds. Mix on low speed just until evenly distributed throughout the nougat. Do not overmix.

Immediately transfer the sticky nougat mixture into the prepared pan using a heat-resistant silicone spatula. Wet your hands slightly or use a second piece of parchment paper to press the nougat firmly and evenly into the pan. It's important to work quickly as the nougat will begin to set.

Place the second sheet of wafer paper on top of the nougat, pressing gently to ensure it adheres.

Let the nougat cool completely at room temperature for at least 2-4 hours, or preferably overnight, until firm. Do not refrigerate, as this can make it too hard and difficult to cut.

Once completely set, lift the nougat from the pan using the parchment paper overhang. Place it on a clean cutting board. Using a sharp knife that has been lightly oiled (this prevents sticking), cut the nougat into desired bar sizes (e.g., 1x2 inch bars). Clean and re-oil the knife periodically.