See below

Mix 1/2 cup sugar, 2 Tbls. cornstarch & dash of salt. Add 1/2 cup
water, 2 Tbls. butter, 2 teapoons grated lemon rind, 3 Tbls. lemon
juice & 3 drops of yellow food coloring. Bring to rolling boil,
stiring constantly; boil & stir 1 minute. Cool.