Combine 1 c. sugar, water and corn syrup in large heavy saucepan. Cook over medium heat, stirring constantly, until clear.
Cook without stirring, until candy thermometer registers 240.
Beat egg whites at high speed with mixer until soft peaks form, continue to beat, adding hot syrup mixture in heavy stream.
Add powdered sugar and lemon extract to mixture. Continue beating until stiff peaks form and frosting is thick enough to spread.
Spread frosting on sides of cake.
Notes
*****If using a metal bowl and heavy duty mixer to beat frosting, it will take 3-4 minutes to reach spreadable consistency. Frosting may take twice as long to thicken if using another type of mixer and glass bowl.
Recipe by Geaux Ask Alice! at https://geauxaskalice.com/tart-lemon-cheese-cake-2/