Key Lime Cake

Key Lime Cake
It is so yummy, I'm sure your friend will love it! It is such a small amount of the milk that I don't worry about it (I keep all of my cakes out unless they have a cream cheese frosting!). If you are worried, you can put it in the fridge but be sure to take out 4+ hours in advance. Enjoy!
Ingredients
For the frosting:

• 6-8 cups powdered sugar
• 3 tablespoons key lime juice (3-4 key limes)
• ¼ cup sweetened condensed milk
• 1-2 tablespoons hot water
• 1.5 cups (3 sticks) unsalted butter, softened
• 1 cup shortening
• 1/4 teaspoon salt
• Green food coloring gel

For the Cake:

• 1/2 teaspoon salt
• 1 cup (2 sticks) unsalted butter, room temperature
• 1 ¾ cups sugar
• 3 cups cake flour
• 1.5 teaspoons baking powder
• 1.5 teaspoons baking soda
• 8 tablespoons key lime juice (8-10 key limes)
• 5 egg whites, room temperature
• ½ cup sour cream, room temperature
• 2 teaspoons vanilla extract
• ½ cup milk, room temperature
• 2 tablespoons vegetable oil

For the Graham Cracker Crumbs:

• 2 cups graham cracker crumbs
• ½ cup 1 stick butter, melted and slightly cooled
• 2 tablespoons sugar

For decoration:

• 1 tablespoon sugar
• Limes slices for garnish
• 1-2 cups heavy whipping cream, cold

Source : asliceofsweet.com