I have a magic bullet and it is great, use it to make shakes all the time in it.

I have eaten ice cream like this many times in the past in the magic bullet, expect I never included lemon juice.

Whenever I plan on having a frozen treat later in the day or at night, I just put some heavy cream, cocoa (I use Hershey's Special Dark), and sweetener (usually a combo of erythritol, xylitol, and splenda) in a container and shake well. Place in the freezer until frozen. It is a really good treat. Like chocolate ice cream. Very low in carbs and quite nutritious with the cocoa.

I find that just using splenda in a cocoa recipe produces a very bitter taste. So that is why I use a combination. Erythritol matches very well with cocoa.

Also, I highly recommend a dark cocoa over regular cocoa in this recipe and all other recipes. There is more of a chocolate and less bitter taste. Also, if you look at the carb count for Hershey's Cocoa and Special Dark, there is only one net carb per serving in Special Dark. While the regular cocoa had two net carbs.