First, in a ramekin, add the dry ingredients - all-purpose flour, sugar, ground cinnamon, and baking powder.
Then add the milk and oil.
Mix well without any lumps. There shouldn't be any dry flour.
Now sprinkle ½ tbsp of sugar on top like below.
Microwave this for 60 seconds / 1 minute or until the cake is done. It should not take more than 90 seconds. I microwaved one cake at a time. Let it cool for 1 to 2 minutes and enjoy right away! Please refer to notes for more details.
The cooking time might vary depending upon your microwave power setting. Test the cake for doneness by inserting the toothpick, and it should come out clean without wet batter. It's ok if the toothpickcomes out clean or with a few crumbs clinging to it.
I tested this recipe in my 900W microwave, and 60 seconds worked perfectly.
I highly recommend ceramic mugs or ramekins for the microwave cakes. Make sure there is sufficient space for the cake to rise.
I used two types of sugar for this recipe. But you can use light or dark sugar for both cake and the topping. Again I strongly suggest using light or dark brown sugar topping for the coffee cake, which gives this streusel topping feel.
Microwave cakes are best when enjoyed fresh.
I kept it nut-free, but you can add ½ tbsp of nuts or top it up with candied nuts.