1 minute Coffee Cake

So the other night I was watching the kids and D starts pulling out all sorts of baking ingredients; flour, brown sugar, butter, eggs. She's making a big mess and I just kind of ignored it because mentally I was done for the night.
But C comes up and asks her "what are you doing?"
All I heard her say was she was making coffee and I got very confused because these picky kids don't like anything, especially coffee.
But C gets really excited and ran over to the cabinet above the Keurig. Then stops. D laughs because he's gone to the wrong cabinet to grab a mug.
I am now very confused so I ask, "you're making coffee? You actually like coffee? You guys don't need coffee at this time of night!"
D corrects me. "Coffee CAKE! In a mug! Its really easy."

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So I went home that night pondering coffee cake in a mug, is it really as good as they made it out to be? They're very picky eaters, maybe this is some really good cake!
I try to stay away from the microwave if at all possible, unless I'm heating up leftovers. I've tried other "minute mug" recipes in the past like chocolate cake and chocolate chip cookie, but they never turn out very good. Usually they're tough and chewy and not very flavorful. The chocolate chip cookie I made was more like a cake than a cookie.
But I decided if coffee cake was good enough for the kids, it's good enough for me.
The first time I did it, it fluffed up very nicely, perfect consistency, but it tasted a bit too eggy for my liking.
The second time around I used half an egg. It did not rise at all and was very dense, but tasted much less eggy.
I am determined to get it right, because it is a very yummy and quick breakfast.

Here's the original recipe, if you want to experiment along with me. I will update once I finally get the perfect result.

-1 tbsp butter
-2 tbsp sugar
-1 egg
-a few drops of vanilla
-1/4 cup flour
-1/8 tsp baking powder
-1 tbsp butter
-2 tbsp flour
-1 tbsp brown sugar
-1/4 tsp cinnamon

Add 1 tbsp butter to a mug and soften in the microwave about 5 seconds (try not to melt it.)
Add sugar and stir until blended.
Add egg and vanilla (you really only need a very little amount of vanilla). Stir.
Add flour and baking powder, stir until smooth.
In separate bowl, combine remaining butter, brown sugar, flour, and cinnamon. Stir until it's a sandy, crumbly consistency.
Pour brown sugar mixture into mug. It looks like a lot but I promise it's not.
Microwave 50-80 seconds depending on your microwave. I've found that exactly a minute is perfect for me.