Lemon Filling for a Doughnut

Instructions

1. 1

   In a medium saucepan, combine the granulated sugar and cornstarch.

2. 2

   Gradually stir in the water until the mixture is smooth.

3. 3

   Cook over medium heat, stirring constantly, until the mixture thickens and begins to boil.

4. 4

   Boil for 1 minute, continuing to stir.

5. 5

   Remove the saucepan from the heat and stir in the lemon zest, lemon juice, and unsalted butter.

6. 6

   Mix until the butter is completely melted and the mixture is smooth.

7. 7

   Allow the lemon filling to cool before using it to fill doughnuts.