In a small bowl, stir together ¼ cup cold water and gelatin. Let stand until softened, about 5 minutes.

In a small saucepan, bring raspberries, sugar, raspberry liqueur, vanilla, and salt to a boil over medium-high heat. Reduce heat and simmer, stirring frequently, about 10 minutes. Transfer raspberry mixture to the container of a blender; process until smooth. Strain mixture through a very fine-mesh sieve to remove any seeds, making sure to retrieve any purée from bottom of sieve. Return raspberry mixture to saucepan; bring to a simmer over medium heat. Add gelatin mixture to raspberry mixture, stirring until gelatin dissolves. Remove from heat; add cream, stirring until well incorporated.

Divide mixture between 6 coupe or gelato glasses. Place glasses on a rimmed baking sheet. Refrigerate until mixture is firm, about 3 hours. Garnish with whipped cream, mint, and raspberries, if desired.