In a large bowl, blend together flour, salt, and a pinch of cinnamon for added warmth. Cut in chilled butter using a pastry cutter until the mixture resembles coarse breadcrumbs. Mix in sugar and one egg to form a cohesive dough. Wrap tightly in plastic wrap and chill for at least 1 hour.

Preheat your oven to 190°C (374°F). Roll out the chilled dough to about ¼ inch thick. Fit into tartlet tins, trim excess, line with parchment paper, and weigh down with baking weights. Bake for 10 minutes, remove weights, then bake for an additional 5 minutes until golden. Cool on wire racks.

Beat egg yolks and sugar in a medium bowl until pale and creamy. Gently heat heavy cream in a saucepan until steaming. Gradually combine warm cream with yolk mixture, stirring constantly. Heat over low, then mix in chopped white chocolate. Allow to cool completely.

Whip another cup of heavy cream to medium-stiff peaks in a clean bowl. Fold whipped cream into cooled white chocolate mixture carefully to preserve airy texture. Refrigerate for about 30 minutes to firm up.

Once tart shells are completely cool, spoon the mousse into each shell, smoothing the tops. Cover with plastic wrap and refrigerate for at least 4 hours, preferably overnight for best results.

When ready to serve, remove from fridge and garnish with fresh berries, chocolate shavings, or mint leaves. Enjoy the beautiful layers of creamy mousse and flaky crust!