In a medium saucepan over medium heat, melt the butter until bubbly and begins to brown, about 3-5 minutes. Whisk in the sugar-free white chocolate and heavy whipping cream until smooth. Remove from heat, then add natural sweetener, vanilla, and salt, stirring until fully combined. Allow to cool slightly, then pour into molds and refrigerate for 1-2 hours until set.

While filling cools, prepare coating by melting additional sugar-free white chocolate in a double boiler over low heat until smooth. Mix in cocoa powder if desired. Set aside.

Carefully remove cooled truffles from molds. Dip each into warm melted coating, allowing excess to drip off. Place on parchment-lined tray, dusting with cocoa powder while wet if desired.

Chill coated truffles in the refrigerator for an additional hour before serving.