In a microwave-safe mug (at least 12oz in size), start by adding the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, and salt. Use a small whisk or a fork to mix these dry ingredients thoroughly until they are fully combined and free of lumps.
Next, pour in the milk, vegetable oil, and vanilla extract to the dry mixture. Stir well until the batter is smooth and all wet ingredients are incorporated evenly into the dry mix, ensuring there are no lumps.
Carefully spoon the tablespoon of creamy peanut butter into the center of the batter. Do not stir it in; this will create a delicious, gooey molten center once baked.
If you fancy an extra chocolatey treat, feel free to sprinkle some chocolate chips over the top of the batter. This optional step enhances flavor and makes the cake even more decadent.
Place the mug in the microwave and cook on high power for 40-60 seconds. Start checking around the 40-second mark to gauge doneness, as microwaves can vary in power. The mug cake should rise and appear set, yet still maintain a soft and slightly gooey center.
Once microwaved, allow your mug cake to cool for about a minute before digging in. Enjoy it straight from the mug for a simple and delicious treat!
Notes
For a delightful finish, top your mug cake with a dollop of whipped cream and a sprinkle of crushed peanuts. Enjoy it warm to savor the rich flavors and gooey center!