1/3 cup sugar
1 tablespoon cornstarch
1 cup water
1 tablespoon unsalted butter
3 tablespoons fresh lemon juice
3 tablespoons fresh lime juice
4 very thin lemon slices
4 very thin lime slices
1 teaspoon vanilla extract
Whisk sugar and cornstarch
in small saucepan to blend. Add 1 cup water and stir over medium heat
until mixture boils and thickens. Remove from heat. Add butter and stir
until melted. Whisk in lemon juice and lime juice. Cool sauce to room
temperature. Stir in lemon and lime slices and vanilla extract. Add one
drop yellow food coloring, if desired.