Pulse flour, powdered sugar, and salt in a food processor. Add cold butter and pulse until coarse. Add egg yolk and ice water, pulsing until dough forms.

Form dough into a disk, wrap in plastic, and chill for 1 hour.

Roll dough and press into a 9-inch tart pan. Freeze for 30 minutes.

Preheat oven to 375°F (190°C). Blind bake the crust with pie weights for 15 minutes, remove weights, and bake 10 more minutes. Cool slightly and lower oven to 325°F (160°C).

Whisk eggs, yolks, and sugar until smooth. Add grapefruit juice, zest, heavy cream, and salt. Whisk until blended and skim off any foam.

Pour the custard into the baked tart shell. Bake at 325°F (160°C) for 30-35 minutes until the center is just set but slightly jiggly.

Cool completely on a wire rack, then chill in the refrigerator for at least 4 hours.

Right before serving, sprinkle an even layer of superfine sugar over the tart. Use a kitchen torch to caramelize the sugar to a deep amber.

Garnish with fresh pink flowers. Slice with a hot, dry knife and serve immediately.