Combine coconut oil, cocoa powder and erythritol and stir until there are no clumps. Add a pinch of salt to help bring out sweetness.
If your coconut butter is not soft enough to spoon and pour, place the jar in a hot water bath. Fill up a bowl with hot water and let the coconut butter jar sit in it for a few minutes. You'll see the butter starting to become very soft along the edges of the jar.
Pour roughly half your chocolate mixture evenly into 4 silicone cupcake molds sitting on a plate. Tilt each cupcake mold around so that the chocolate mixture coats the edges a little. This will help hide the white layer of coconut butter. (This method works very well with paper liners, but as silicone ones are very nonstick, you'll still see some coconut butter peeking out from the sides.) Place in freezer for about 5 minutes.
When the bottom layer has hardened, spoon a teaspoon of coconut butter onto each mold. Tap the plate of cupcake molds on your counter a few times so the coconut butter spreads out evenly and covered the whole chocolate layer. Place again in the freezer for a few minutes.
Lastly, take the remaining chocolate mixture and cover the hardened coconut butter. Freeze one last time for about 5 more minutes. Enjoy!