- 2 1/4 teaspoons unflavored gelatin
- 1/2 cup cold water
- 2 (1/2 pound) firm-ripe California avocados, quartered, pitted, and peeled
- 1 1/2 cups sour cream
- 1 1/2 tablespoons fresh lemon juice
- 1/2 teaspoon grated onion
- 1 teaspoon salt
- 1/4 teaspoon white pepper
- Accompaniment: crackers
- Sprinkle gelatin over cold water in a small heavy saucepan and let soften 1 minute. Cook over low heat, 1 to 2 minutes, then remove from heat.
- Coarsely mash avocados with a fork in a large bowl. Stir in gelatin mixture along with remaining ingredients until combined well.
- Pour mixture into lightly oiled mold and chill, covered tightly with plastic wrap, until firm, at least 4 hours.
- Run tip of a thin knife between mold and mousse. Tilt mold sideways and tap side of mold against a work surface, turning it, to evenly break seal and loosen mousse. Keeping mold tilted, invert a plate over mold, then invert mousse onto plate.