Make the cupcakes: Preheat the oven to 350 degrees F. Line 18 muffin cups with paper liners. Sift the flour, baking powder and salt into a medium bowl; set aside. Beat the egg whites in a large bowl with a mixer on medium-high speed until stiff peaks form, about 4 minutes; set aside.
Beat the butter, granulated sugar, egg yolks, orange zest and orange oil in a separate large bowl with a mixer on medium speed until smooth and combined, about 4 minutes. Reduce the speed to low; beat in the flour mixture in three batches, alternating with the orange juice. Fold in the beaten egg whites. Spoon the batter into the muffin cups, filling each about halfway. Bake until a toothpick inserted into the centers comes out clean, about 15 minutes. Let cool 10 minutes in the pans, then remove to racks to cool completely.
Make the frosting: Beat the butter and vanilla in a large bowl with a mixer on medium-high speed until light and fluffy, about 6 minutes. Reduce the speed to low; gradually beat in the confectioners' sugar. Add the milk, increase the speed to medium and beat until light and fluffy. Frost the cupcakes. Top with sanding sugar and orange gummy candies.
Orange oil gives the cupcakes an intense orange flavor that you can?t get from just extract or zest.
Photograph by Andrew Purcell