Preheat the oven to 375 (F) -- this is a 50 (F)-degree increase from the original recipe temperature of 325 (F).
Put the flour, sugar, baking powder, lemon zest, and butter in a freestanding electric mixer with a paddle attachment (or use a handheld electric whisk) and beat on slow speed until you get a sandy consistency and everything is combined.
Gradually pour in the milk and beat until just incorporated.
Add the egg to the flour mixture and continue beating until the flour is just incorporated, making sure to scrape any unmixed ingredients from the side of the bowl with a rubber spatula. Continue mixing for a couple of minutes until the batter is smooth, but be careful not to overmix.
Using a cookie scoop, spoon 2 tablespoons of the batter into cupcake cases (or, fill until the case is two-thirds full). Bake in the preheated for 20-25 miutes, or until the cake bounces back when touched. A skewer inserted in the center should come out clean.
Let the cupcakes cool slightly in the pan before turning out into a wire rack to cool completely.
When the cupcakes are cold, spoon the lemon frosting on top and use extra lemon zest to decorate accordingly.