*For best results, I recommend natural cocoa powder, not Dutch process. If using Dutch process cocoa powder, however, replace the baking soda with ¼ teaspoon baking powder or use the ⅛ teaspoon baking soda and add ¼ teaspoon white or apple cider vinegar. Dutch process cocoa powder is less acidic/has higher pH, so this change is needed to create a similar rise.
**Can I use a different sweetener? Any granulated sweetener will work, so long as the quantity is the same, as the bulk is needed. So, a cup-for-cup sugar substitute would work, but a pinch of concentrated stevia would not. Brown sugar could also be used, while honey and maple syrup would make the batter too runny.
***No peanut butter powder? Finely ground almond flour works well. All-purpose flour creates an airier crumb and the perception of a drier cake. Protein powder may also be used; note that a flavored variety will slightly alter the taste (which you may like!).
Chocolate chip tips: Standard-size morsels may be used; they will sink to the bottom and create a melted chocolate layer. If you flip the cake onto a plate, it’s sort of like icing. Standard-size chips may also be dotted on top of the mug cake as soon as it’s done cooking. The hot cake will melt the bottom of the chips and make them stick. (see photos)
Mix it up:
• Feel free to substitute peanut butter, dark, or white chocolate chips. If doing so, however, roughly chop them before using to prevent the sinking mentioned above.
• For an extra hint of salty-sweet flavor, sprinkle the finished muffin with a small pinch of flaky sea salt immediately upon removing from microwave.
• Instead of the molten center, you could “frost” the finished mug cake with peanut butter.