First melt your chocolate chips in a small pot or in the microwave. A stove-top with a double-boiler is the safest way to not burn the chocolate, but you can do it directly over low heat or with the microwave if you are careful and stir frequently. Once the chips are melted, add the cocoa powder, mix well and set aside.
Warm sweetener, vita fiber, heavy cream, and 1/3 cup of water in a medium heavy-bottomed pot over low heat without stirring until sugar dissolves. Increase heat to medium high, stirring frequently. It will bubble up once it get's really hot and that's exactly what you want! Let it bubble for about 4-5 minutes, stirring it constantly so as not to burn.
Turn off heat and whisk in the salted butter, vanilla and melted chocolate. It will look messy at first but will come together beautiful and creamy but thick like real fudge should be. I would not keep this in the fridge, or you'll be getting your hammer out just to get some. It keeps beautifully on the counter and is much easier to get into... :)