In ramekin or mug, add butter and soften in microwave for 10 to 15 seconds. Using a different size and/or type of cups of ramekins may affect cooking time.
Add sugar, brown sugar, vanilla extract, and egg yolk; mix together with fork.
Stir in flour, baking soda, and salt. Texture should be consistency you would expect for cookie dough. Stir in the chocolate chips.
Place in microwave and cook at high heat for 40 to 60 seconds. Start checking for doneness at 40 seconds. Do not go over 60 seconds or cookie will burn and get rock hard!
Best served warm. Enjoy!
Variation: Add 1 tablespoon of creamy peanut butter to make a delicious Peanut Butter Chocolate Chip Mug Cookie.
Microwave Chocolate Chip Cookies in a Mug Recipe: https://whatscookingamerica.net/cookie/mug-chocolatechipcookies.htm