Pour in egg yolk, melted butter, vanilla extract, brown sugar and salt into a mug. Mix well.
Next, pour 3 tbsp of all-purpose flour and � tsp of baking powder along with 2 tbsp of chocolate chips. Continue to mix until it turns into a dough and then flatten it.
Microwave for 1 minute.
Optional: Place one scoop of vanilla ice cream to top off your Cookie in a Mug! It�s perfect when your cookie is still warm and fresh!