Add the flour, sugar, cocoa powder, baking powder, and salt to a mug. Stir to combine.
Pour in the oil, milk, vanilla, chocolate chips, and stir until a smooth batter forms.
Optional: You can place one tablespoon of peanut butter, Biscoff, or Nutella in the center of the batter and cover with a bit of batter before cooking the cake.
Cook in the microwave for 60 seconds. Let it set in the microwave for 1 minute with the door closed.
If the cake is still raw in the center microwave for another 15 seconds, since all microwaves work different.
Notes
Baking in the Oven: If you don't have a microwave, no worries, bake in the oven at 350ºF in a greased oven-safe ramekin for 15 minutes.You can make the batter in a separate bowl, and grease the mug with oil spray before adding the batter in, if you wish to remove the cake from the mug before serving it.Sweetener: Use 1 tbsp of honey instead of sugar. You can use 2 tsp of stevia instead of sugar. Or simply lower the sugar amount to 1 1/2 tbsp if you like the cake to be on the less sweet side.Milk: you can use any dairy free milk of your choice instead of regular milk to make a dairy-free version.