I made this cake for a Relief Society activity, and it was a hit!  Some people were asking for the recipe, so I’ll just post it here so it’s accessible.  You can control how lemony you want it! I like VERY lemony.  I didn’t use food colouring, but you could if you want it more yellow.
2016-03-17 18.25.19
-1 (18.25 ounce) package yellow cake mix
-1 (3.4 ounce) package instant lemon pudding mix
-1 3/4 cups water
-3 egg whites
Preheat oven to 350 degrees.  Spray a 10×15 inch pan with non-stick cooking spray
In a large bowl, mix together cake mix and pudding mix. Pour in water and egg whites.  Beat on low for 1 minute.  Increase speed to high and beat for 4 minutes.  Pour batter into prepared 10×15 inch pan.
Bake in preheated over for 25-30 minutes, or until toothpick inserted into center of cake comes out clean.  Allow to cool completely.
Lemon filling
-3/4 cup granulated sugar
-2 Tbsp cornstarch
-1/8 tsp salt
-3/4 cup cold water
-2 egg yolks (slightly beaten)
-1 tsp grated lemon peel
-3 Tbsp medium lemon
-1 Tbsp butter or margarine
In a small saucepan, combine sugar, cornstarch, and salt.  Gradually add water and whisk until blended.  Whisk in egg yolks, lemon peel, and lemon juice.  Cook over medium heat, whisking constantly until thick and bubbly.  Boil 1 minute, remove from heat.  Stir in butter. Cool to room temperature, without stirring.
Lemon buttercream
-1 cup butter
-6 cups confectioners sugar
-Zest from 1 lemon
-Juice from one lemon
-Lemon extract and milk
Cream butter.  Blend in sugar, beating well with each addition.  Blend in lemon zest and juice.  Add lemon extract and milk as needed to reach desired taste and consistency.
To assemble, cut the cake in half horizontally.  Spread lemon filling over bottom layer, then place top layer back on.  Frost with lemon buttercream.