First, Butterbeer cupcakes.
(This picture is a mix of pumpkin cupcakes shared here on the top two levels and butterbeer on the bottom)
These butterbeer cupcakes are wonderful! They have cream soda and brown sugar in the cupcake (which is a terrific cupcake all by itself by the way, very moist), a butterscotch ganache filing, and butterscotch buttercream with some of the ganache drizzled on top. If you like butterscotch, you will love these cupcakes. I followed the recipe here on Amy Bites.
The other dessert I served with this tea were the pumpkin pasties. I found this recipe on harrypotterrecipes.net. These were also good--they are pumpkin handpies. The website has all different sorts of Harry Potter themed recipes, if you want to take a look for ideas for your own tea party!