Homemade keto muskateer candy bars

Contents
3 ounces unsweetened chocolate, chopped
2 ounces unsweetened white chocolate, chopped
1 ounce cocoa butter
½ tablespoon unsalted butter
1 teaspoon powdered erythritol
⅛ teaspoon raw stevia
a pinch of salt
2 ounces egg whites
½ tablespoon cocoa powder
⅛ teaspoon xanthan gum
⅛ teaspoon powdered erythritol