I tested this recipe using margarine and then again with real butter. Believe me, browned margarine tastes absolutely nothing like browned butter. Definitely worth the extra $2 for real butter to get that delicious caramely flavor.
When you're browning the butter, use a pan with a light colored finish so you can keep track of how dark your butter is getting. It can happen pretty quickly. And if you don't have cake flour on hand, substitute the cake flour with 1-1/2 c. all-purpose flour plus 2 T. potato (or corn) starch.
And to top it all off, these cupcakes deserved more than just a boring old spiced buttercream. These babies were covered with pumpkin pie. Yes, I said it. Actual pumpkin pie. You just prepare and bake pumpkin pie filling/custard stuff as normal, without the crust. Once it's done baking and has cooled, stir it up until smooth and pipe it onto your cupcakes. Thanks for that idea, too, Cupcake Project! These were delicious and perfect for the start of fall!