1. Drain pineapple, reserving 1/4 cup juice. Set crushed pineapple aside.
2. In double-boiler top, with portable mixer at high speed, beat egg yolks, sugar, and salt until very thick, about 5 minutes. Stir cassis and reserved pineapple juice into beaten egg yolks.
3. Place double-boiler top over hot, not boiling, water in double-boiler bottom. Cook, beating constantly at medium speed, until mixture is fluffy and warm, and mounds slightly when beater is lifted, about 5 minutes.
4. Remove double-boiler top from double-boiler bottom; fold in reserved crushed pineapple. Spoon warm sauce into dessert bowls and top with ice cream, sherbet, or fresh berries or spoon over dessert crepes.