Make and refrigerate the sauce up to two days ahead and the panna cotta up to a day ahead. Look for almond milk in aseptic containers on the organic food aisle of your supermarket. If you can't find it, substitute whole milk.
1 envelope unflavored gelatin
1 2/3 cups almond milk (such as Almond Breeze), divided
2/3 cup half-and-half
1/3 cup sugar
1 (6-inch) piece vanilla bean, split lengthwise and divided
1 1/2 cups mango nectar
1 tablespoon fresh lime juice
Fresh raspberries (optional)
How to Make It
Sprinkle gelatin over 1/3 cup almond milk in a small bowl; let stand 4 minutes.
Combine 1 1/3 cups of almond milk, half-and-half, sugar, and half of the vanilla bean in a medium saucepan; bring to a simmer over medium heat (do not boil). Remove from heat. Add gelatin mixture, stirring until the gelatin dissolves. Remove vanilla bean. Pour mixture evenly into 6 (6-ounce) custard cups coated with cooking spray. Cover and chill 8 hours or overnight.
Combine remaining half of the vanilla bean and nectar in a small saucepan; bring to a boil. Reduce heat to medium, and cook until reduced to 1 cup (about 15 minutes). Remove from heat; stir in lime juice. Cover and chill.
Loosen edges of custards with a knife or rubber spatula. Place a dessert plate, upside down, on top of each cup; invert onto plates. Spoon the sauce around custards. Garnish with fresh raspberries, if desired.