In a mixing bowl, beat the egg yolks with granulated sugar until pale and thick, about 3 minutes. Warm ¼ cup of heavy cream in a saucepan over low heat until small bubbles form, then add it to the egg mixture, stirring constantly.

Return the mixture to the saucepan and cook over low heat for about 5 minutes, stirring until it thickly coats the back of a spoon. Remove from heat and let cool slightly.

Chop the white chocolate and add it to the warm egg-custard mixture, stirring until melted and smooth. Let cool to room temperature.

In a separate bowl, whip the heavy cream until medium-stiff peaks form, about 3-4 minutes.

Gently fold in the whipped cream into the white chocolate mixture in three additions until no streaks remain.

In a food processor, pulse together the flour, salt, cayenne pepper, cinnamon, and cold unsalted butter until it resembles coarse breadcrumbs.

Add granulated sugar and eggs to the crumbly mixture, pulsing until dough forms. Wrap in plastic wrap and refrigerate for at least 1 hour.

Preheat oven to 190 °C (375 °F). Roll out chilled dough and place in a tart pan, cover with parchment paper and weights, and blind bake for 10 minutes. Remove weights and bake for an additional 5 minutes.

Allow the baked crust to cool completely in the pan on a wire rack.

Pour the white chocolate mousse mixture into the cooled crust and refrigerate for at least 4 hours.

Garnish with white chocolate shavings, fresh berries, or edible flowers before serving. Slice carefully and serve chilled.