Lemon Curd

One of our church members gave us a wonderful pound cake.  Every year, I freeze it until all the Christmas cookies and fudge are gone and then I bring it out to enjoy.  We had several pieces with strawberries and whipped cream, and several pieces just plain.  I decided to make some lemon curd to go over the top for the rest to give a little variety.  This is Alton Brown's recipe from Food Network.
Ingredients:
5 egg yolks
1 cup sugar
4 lemons zested and juiced (to = 1/3 cup)
1 stick butter
Add about an 1 1/2 inches of water to the bottom of a double boiler. Bring water to a simmer over medium-high heat. Meanwhile, combine egg yolk and sugar in the top of the double boiler off the heat.  Whisk about 1 minute. Measure lemon juice and zest to get 1/3 cup.  Add it to the egg yolk mixture. Whisk to combine.  When the water reaches a simmer, reduce heat and place the mixture over the indirect heat of the double boiler.  Wisk for about 8 minutes or until mixture is thick enough to coat the back of a spoon. Remove from heat and add butter a piece at a time, allowing each piece to melt before adding the next piece. Place the curd in a clean bowl and cover by laying plastic wrap directly on the surface of the curd. Refrigerate up to two weeks.