Preheat oven to 350 degrees F and grease (3) 9-inch cake pans with pam baking spray.
In a large bowl, combine the flour, baking soda, baking powder and salt.
In another large bowl, cream butter, vanilla, and sugar. Stir in lime juice, tequila, and lime zest. Stir in egg whites.
Gradually add dry ingredients a little at a time until just combined.
Evenly divide the batter between the 3 cake pans.
Bake for 25-30 minutes. Cool completely.
For the Frosting
In a large bowl combine all ingredients. Mix until smooth.
Assembly
Scoop around 1 cup of frosting onto the first cake layer and spread until smooth. and smooth evenly
Repeat with the second layer. Then top with the third layer.
Frost the sides and top of the cake. Pipe dollops of icing using a star tip if desired.
Notes
Ingredient Notes and Shopping Tips
Baking Soda and Baking Powder: Be sure to replace these ingredients every 6-12 months as they can lose their effectiveness.
Butter: If you don't have unsalted butter on hand, use salted butter and omit the added salt.
Egg Whites: Separate eggs by pouring them back and forth between the shells. There are also a number of egg-separating gadgets out there.
Tequila: Use a mid-shelf brand you enjoy drinking. I like Patron or Jose Cuervo.
Milk: Use whole milk for the best results.
Lime Juice: Use freshly squeezed lime juice if possible. The bottled stuff tends to be too acidic and can taste artificial.
Tips
Non-Alcoholic: Replace the tequila with additional milk to make this treat nonalcoholic.
Zest: Be sure to zest just the green part of the lime. The white pith underneath is bitter.
Juice: Microwave for 20-30 seconds, then roll the lime on the counter to get the most juice possible. If you don't have a juicer, use your muscles and give each lime half a good, hard squeeze.
Cake Board: Build your cake on a cake board for easy transport.
Cake Leveler: Get flat cake by layers using a cake leveler to cut off the domes.