• If you’re making the frosting, brown 75g of butter. Set aside to cool. This takes a while so I like to do it before I even start my cupcakes.  Check out how to brown butter if you need help with this step! 
• Preheat oven to 350 F. Line 2 cupcake pans with 15 cupcake liners in total. 
• In your stand mixer or a large mixing bowl, add cake flour, baking soda, baking powder, white sugar, brown sugar, cinnamon, nutmeg, ginger, and salt. Mix until combined. 
• Slice your butter into 8 or so slices and add butter to the flour mixture one slice at a time. Beat until the mixture is the consistency of wet sand. 
• In a separate bowl, combine egg whites, rum, milk, vanilla, and sour cream. Mix with a fork or whisk until there are no more big chunks of egg whites and sour cream. 
• Slowly add in the wet ingredients to your bowl containing the flour mixture. Mix everything until just combined. 
• Fill the cupcakes about 2/3rds of the way full. Bake at 350 F for 15-18 minutes. Test that the cupcakes are done by gently pressing the top. If it springs back, the cupcakes are ready. If it leaves a dent, bake them for another 2 minutes at a time.
• Once completely baked, set the cupcakes aside to cool completely. When you’re ready to frost them use a fork to poke holes in each cupcake. Then, pour ¼ tsp of spiced rum over each cupcake. 

For The Brown Butter Frosting

• If you haven’t already, brown 75g of butter and set aside to cool completely. This will take about 30 minutes. 
• Take the other 75g of softened butter and beat on a medium-high speed until pale and fluffy (about 5 minutes). 
• Add brown butter into the mixing bowl when it’s completely cool. Mix the two butters together. It will look a little lumpy at first, but it will correct itself later. 
• Add in vanilla, 2 tbs of rum, and half the powdered sugar. Mix until almost combined. 
• Keep adding the rest of the powdered sugar until you get your desired consistency. If you want to thin out the frosting, you can add more rum or milk 1 tsp at a time. 
• Frost and enjoy!