Line an 8-inch square pan with parchment paper, letting some paper hang over the edges to use as a handle later.

In a medium saucepan over medium heat, combine the sugar, corn syrup, and 1/2 cup water. Stir until the sugar is dissolved.

Continue to cook the mixture until it reaches 240°F on a candy thermometer.

In a separate bowl, beat the egg whites until stiff peaks form, about 5 minutes with an electric mixer.

Once the sugar syrup reaches the right temperature, slowly pour it into the beaten egg whites while the mixer is running.

Mix until well combined, then stir in the vanilla extract, chopped nuts, and mini marshmallows.

Quickly pour the nougat mixture into the prepared pan, smoothing the top with a spatula. Allow it to cool completely at room temperature.

Once cooled, melt the chocolate and pour it over the nougat. Allow it to set before using the parchment papers as handles to lift it out of the pan.

Finally, slice the nougat bars into bite-sized pieces, and enjoy!