Special equipment: eight 4- to 6-ounce serving glasses
For the panna cotta: Place 1/2 cup water in a small bowl and sprinkle over the gelatin; set aside to soften.
In a small saucepan, add the half-and-half, heavy cream, white chocolate and sugar, and bring to a simmer over medium heat just long enough for the chocolate to melt. Turn the heat off and add the gelatin mixture; whisk for a couple minutes or until the gelatin melts. Strain, then add the vanilla extract to the strained mixture.
Divide the mixture among 8 serving glasses, putting 4 ounces of the mixture in each glass; cover and refrigerate 4 hours or overnight.
For the raspberry sauce: Place the raspberries, sugar and lemon juice in a blender and puree until smooth. Strain through a fine-mesh sieve into a small saucepan.
Stir the cornstarch together with 3 tablespoons of water in a small bowl. Bring the puree to a simmer and add the cornstarch mixture. Cook, stirring constantly, until the mixture thickens. Remove from the heat and pour it in a small container. Let cool completely.
To serve: Pour a little raspberry sauce over each panna cotta and top with a few raspberries, white chocolate shavings and a sprig of fresh mint.