In a medium-sized saucepan, stir together the granulated Erythritol with the liquid Erythritol, vanilla, and salt until evenly mixed. Place over medium-high heat and cook without stirring for about 3 minutes, until golden and bubbly or until a candy thermometer inserted into the mixture reaches 104ºC/220ºF.
In the meantime, pour the egg whites in a large bowl. Add the lemon juice and beat the egg whites on medium speed until stiff peaks form.
Increase the mixer speed to very high. Gradually add the hot syrup, in a stream, into the egg whites. Beat until the mixture gets very thick and glossy for about 8-10 minutes. Fold in the toasted walnuts.
Preheat the oven to 140ºF.
Line a baking sheet with baking paper and pour in the mixture.
Allow to dry in the preheated oven at 140ºF for 2 hours.
Using a wet knife, cut it into 24 pieces and allow it to cool before serving.