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 comes to a boil.

4. 4

   Boil for 1 minute, then remove from heat.

5. 5

   Stir in the lemon zest, lemon juice, and unsalted butter until the butter is melted and the mixture is smooth.

6. 6

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