Incredibly rich chocolate buttercream frosting

I think I've come up with a frosting to accompany that orange cake recipe I published the other day.  A word of warning though - this is incredibly rich and decadent, and of course not exactly "hard core paleo" given that it's made with butter.  But the orange cake accompanies this frosting quite nicely, and I think I'll be looking for occasions to make this in the future.  The recipe is based off of this one, but I've altered the sweeteners a bit.

Ingredients

• 1 cup (2 sticks) butter, salted
• 1/2 cup erythritol
• 1/2 cup "spoonable" stevia
• 2/3 cup good-quality cocoa powder
• 1/4 cup unsweetened chocolate almond milk
• 2 tsp vanilla extract
• 1 tsp chocolate stevia liquid

Instructions

1. Cream the butter in a stand mixer (or use a bowl and a hand mixer).
2. Add in the erythritol, spoonable stevia, and cocoa powder, and combine well.
3. Add the almond milk slowly, making sure it's combined well with the mixture.
4. Blend in the vanilla extract and liquid stevia.
5. Ice your cake!