|Sugar||1⁄2 Cup (8 tbs)|
|Cornstarch||1 1⁄2 Tablespoon|
|Water||3⁄4 Cup (12 tbs)|
|Lemon juice||1⁄3 Cup (5.33 tbs)|
|Grated lemon rind||1 1⁄2 Teaspoon|
|Yellow food coloring||3 Drop|
Combine sugar, cornstarch, and salt in a small saucepan.
Combine water, lemon juice, and egg yolk, stirring well, add to sugar mixture.
Cook over low heat, stirring constantly, until mixture comes to a boil and thickens.
Stir in butter, lemon rind, and food coloring, if desired, let cool slightly.
Spread over cake.