In small saucepan, stir together sugar and cornstarch. Stir in pineapple juice until throughly blended. Cook over medium heat, stirring constantly, until mixture boils. Stir a little of the hot mixture into eggs, then stir back into hot mixture. Reduce heat to low and stir until mixture bubbles, about 2 minutes. Stir in lemon juice.

Spoon into 6 (6 oz.) custard cups or gelatin molds. Freeze several hours or overnight.

To serve, spoon about 2 1/2 tablespoons puree onto each plate and gently place unmolded frosties in center.