In a mug, with a fork, mix together all of the dry ingredients (baking blend, sweetener, cocoa powder, baking powder, and salt).
Add the wet ingredients (sour cream, heavy cream, egg yolk, extracts, and butter) and mix with the fork until thoroughly incorporated. Also mix in a teaspoon or so of chopped hazelnuts if you want.
Pop in the microwave and nuke on high for 1 and 1/2 minutes. Or, bake in the oven at 350° F for 10 or more minutes till done (be sure to use an oven safe mug or a small dish that is oven safe).