In a mixing bowl, combine flour and powdered sugar. Add cold butter and mix until crumbly.

Add egg yolk and cold water, mixing until a dough forms. Wrap in plastic and refrigerate for 30 minutes.

Preheat oven to 350°F (175°C). Roll out dough and cut into circles to fit tartlet pans.

Press dough into pans and prick the bottoms with a fork. Bake for 15 minutes or until golden. Let cool.

Melt white chocolate in a double boiler, stirring until smooth. Remove from heat and let cool slightly.

In a small bowl, dissolve gelatin in water (if using) and let sit for 5 minutes.

In a separate bowl, whip heavy cream, sugar, and vanilla until soft peaks form.

Fold melted chocolate into whipped cream gently. If using gelatin, heat until dissolved and fold in.

Spoon mousse into cooled tartlet shells, smoothing the tops.

Chill in the refrigerator for at least 2 hours until set.

Before serving, garnish with fresh raspberries and white chocolate shavings.