1. Prepare the Crust:

1. In a small bowl, sprinkle 1 1/2 teaspoons gelatin over 3 tablespoons cold water. Let bloom for 5 minutes.
2. In a saucepan, combine plum puree and 1/4 cup sugar. Cook over medium heat until slightly thickened, about 5 minutes. Remove from heat and stir in vanilla bean paste and bloomed gelatin until dissolved. Let cool to room temperature.
3. In a stand mixer, whip cold heavy cream to soft peaks. Gently fold in the cooled plum mixture until combined.
4. Fold in the melted white chocolate until just combined. Pour into heart-shaped silicone molds. Freeze for at least 4 hours or until solid.
5. For the mirror glaze: In a small bowl, sprinkle 1 1/2 teaspoons gelatin over 3 tablespoons cold water. Let bloom.
6. In a saucepan, combine 1 1/2 cups sugar and 2/3 cup water. Bring to a boil, stirring until sugar dissolves. Remove from heat and stir in sweetened condensed milk and bloomed gelatin until smooth.
7. Stir in vanilla extract. Let glaze cool to about 90°F (32°C). Optional: mix in a pinch of silver luster dust for shimmer.
8. Line a wire rack with a baking sheet. Place frozen hearts on the rack. Pour the warm mirror glaze over each heart, ensuring full coverage. Let set for 2 minutes.
9. Carefully transfer hearts to serving plates. Let thaw in refrigerator for 15 minutes before serving for a silky texture.