For the frosting: Reduce the ½ cup lemon juice to 3 tablespoons by simmering it and letting it evaporate. This will concentrate the flavor. Cool the reduction to room temperature.
Make Fluffy Vanilla frosting but mix the lemon reduction into the butter before adding the confectioners sugar. Add the extra ¾ cup confectioners sugar at the end. Tint to desired color with yellow food coloring. Use immediately or store airtight at room temperature for one day, chilled for a week.
For the cake: Slice each cake layer in half to make 4 cake layers. Place 1 layer on your cake plate or platter and top with ¼ cup lemon curd, spread evenly. Top with a spoonful of Lemon Frosting and spread over the curd; top with second cake layer. Spread that layer with lemon curd and frosting and repeat one more time with the third layer. Top with the last layer.
My secret? A lemon juice reduction. Made in a matter of minutes, this fresh juice reduction is a super concentrated lemon bonanza, that is added to my frosting. The genius here is that because it's concentrated and reduced, it doesn't add a lot of liquid to my frosting. I still end up with fluffy frosting instead of a runny glaze, or frosting that loses it's flavor because you had to add too much confectioners' sugar.