A stand mixer is ideal and will get your frosting silky smooth. In a large bowl add the room temperature butter. Beat with an electric mixer on high for 5 minutes till fluffy and white in color. Add the powdered sweetener of choice and beat it on the lowest setting for a minute, or until the sweetener is completely mixed in with the whipped butter.
There are other Low Carb Sweetener available (like Confectioners Swerve) that are extremely suited to make frosting. Make sure the sweetener you use is an exact 1:1 sugar replacement, or else the sweetness will be off balanced. If you have only a granulated sugar, run it in the food processor to get a powdered texture.
If you have only a granulated sugar, run it in the food processor to get a powdered texture. Using plain granulated sweetener won’t work for this frosting will make the frosting gritty. Buttercream frosting, low carb or full sugar, always work best if you use a high powered mixer.