As a rule, a CTE will NEVER improve performance. A CTE is essentially a disposable view. There are no additional statistics stored, no indexes, etc. It functions as a shorthand for a subquery. In my opinion they can be EASILY overused (I see a lot of overuse in code in my job).
Check the cupcakes at the minimum baking time. If the recommended baking time is 18-22 minutes, check them at 17 or 18 minutes (just a quick peek, make sure not to let too much heat out of the oven). If the tops are rounded and no long appear wet, they may be done.
Insert six paper cupcake liners into a cupcake pan. Divide the batter evenly into the cups. Bake at 350 degrees Fahrenheit (preheated) for 12 to 15 minutes. Check continually to make sure they do not brown and overcook. Use a wooden toothpick to test if the inside batter is cooked. (Insert the toothpick into the middle of the cupcake.