Sour Lemon Sauce
- 1 1/2 cups sugar
- 3 tablespoons cornstarch
- Pinch of salt
- 2 1/2 cups warm water (about 110 degrees)
- 7 tablespoons unsalted butter, cut into pieces
- Zest of 2 lemons, plus 1/2 cup fresh lemon juice
Bring sugar, cornstarch, salt, and warm water to a boil in a medium saucepan set over high heat, whisking constantly. Cook, whisking constantly, until mixture thickens, about 5 minutes more.
Stir in butter and lemon zest and juice. Cook, whisking, until smooth, 2 to 3 minutes more. Remove from heat; transfer to a medium bowl to cool completely before putting into jars. Sauce can be refrigerated up to 2 weeks.