Combine flour, cornstarch, and lemon juice in a 2-quart saucepan.

Stir until well blended.

Add crushed pineapple with juice, egg yolks, and sugar to the saucepan.

Mix all ingredients thoroughly.

Cook over medium-high heat for 5-6 minutes, stirring constantly.

Continue stirring until the mixture thickens.

Boil the mixture for 1 minute, stirring continuously.

Remove the saucepan from heat.

Allow the mixture to cool for 2-3 minutes.

In a medium-sized bowl, use an electric mixer at high speed to beat the egg whites until stiff peaks form.

Gently fold the pineapple mixture into the beaten egg whites until just combined.

Spoon the pudding into 8 sundae cups.

Chill the cups in the refrigerator until set.

Garnish with pineapple slices cut in half before serving, if desired.