Key Lime Cake

I love icebox pies, and this cake has a delicious filling just like one. Southern Living has from scratch recipes to go with it but I've always just used a mix: the filling is what's important.

• 1 box white cake mix, plus eggs, oil, etc. according to directions
  
• 1/4 cup corn starch
  
• 3/4 cup milk
  
• 3 eggs, or 2 eggs plus 3 yolks
  
• 1 can sweetened condensed milk
  
• 1-2 drops each of yellow and green food coloring
  
• 1/2 cup lime juice*
  
• 3 tablespoons butter
  
• 1 tablespoon grated lime rind*
  

Prepare cake mix according to package, expect bake in two 13" x 9" pans for about 15 minutes or until cake tests done. Cut each layer in half down middle to get 4 nearly square halves. Cool cake layers and set aside.

Dissolve corn starch in cold milk in saucepan. Whisk in sweetened condensed milk, eggs, lime juice and food coloring. Cook to boiling over medium heat, whisking continuously. Boil one minute, remove from heat and stir in lime rind and butter until butter melts. Fill sink half full with ice water, put pan in until mixture is chilled.  Stir occasionally. Filling should be very thick, almost like frosting.

Top first layer with 1/3 of filling, place next layer on top.  Continue until you have four layers cake and 3 of filling, Wrap in plastic and chill several hours or overnight before frosting. Cake may be frozen at this step and frosted up to a month later.

*to make orange or lemon instead, substitute equal parts lemon juice or orange juice concentrate and lemon or orange rind.  Adjust food coloring appropriately.

Frost with appropriate buttercream frosting or the cream cheese frosting from my carrot cake recipe.

Buttercream frosting

• 1 stick butter
  
• 16 oz powdered sugar
  
• 1/2 cup milk
  
• 2 tablespoons appropriate citrus fruit rind
  

Beat butter until fluffy, add one cup powdered sugar and blend. Mix in milk and rind. Gradually beat in remaining sugar until you have a fluffy icing. Add rind and stir. Frost all sides and top of cake.