In a large bowl, combine flour, salt, and cinnamon. Cut in the chilled butter until the mixture resembles coarse crumbs. Add sugar and egg, mixing until the dough just comes together. Chill for at least 1 hour.

Preheat your oven to 190°C (374°F). Roll out the chilled pastry dough, press into tartlet tins, and bake covered with parchment and pie weights for 10 minutes, then uncovered for another 5 until golden.

In a mixing bowl, beat the egg yolks and sugar until pale. Gently warm heavy cream in a saucepan, then slowly incorporate into the yolk mixture. Return to heat and stir until thickened. Combine with melted white chocolate.

Whip the remaining heavy cream to medium-stiff peaks and gently fold into the cooled chocolate mixture. Refrigerate for about 30 minutes to firm up.

Fill the cooled tart shells with mousse, smooth the tops, cover, and chill for at least 4 hours or overnight.

Garnish with fresh berries or chocolate drizzle before serving. Slice and enjoy!