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.
Use two mini cupcake pans at the same time to speed up the process. Follow the same steps, but fill two pans and place each on a different oven rack. When you rotate the cupcake pans 180 degrees, 10 minutes into cooking, also swap the pans so the one on the top rack is on the bottom, and vice versa.