In a large bowl (or a stand mixer fitted with the paddle attachment), beat the butter, corn starch, sugar, salt and orange zest until fully combined, about 2 min. Add the eggs and yolks one at a time, beating each until fully incorporated. Turn the mixer to low and stir in the blood orange juice. The mixture will look curdled, but it will smooth out as it cooks.

Pour the mixture into a 3 quart heavy-bottomed saucepan and stir in the hibiscus petals. Cook over low heat, stirring constantly, until the mixture is thickened, about 10 minutes. The curd will thicken at about 170º F, or just below simmer. Remove from the heat and pour into a heat-proof bowl, scraping out any curd or hibiscus stuck to the bottom. Allow the hot curd to steep with the hibiscus petals for about 10 minutes, then pour it through the fine-mesh sieve into another bowl or an airtight container, pressing down on the solids to push the curd through. Make sure to scrape the curd from underside of the strainer. Allow to cool to room temperature, then cover the bowl with plastic wrap or seal the container, and refrigerate until chilled, at least an hour. Curd will get thicker as it cools.

Preheat the oven to 350ºF and set a rack in the middle. Line a baking tray with foil and set it aside. To a medium bowl (or the bowl of the food processor if you ground the cookies up), add the cookie crumbs, melted butter, brown sugar, ginger and salt. Mix until completely combined, then tip into a 9-inch round tart pan with a removable bottom. Using your fingers or the bottom of a measuring cup, press the crumbs into the bottom of the pan and up the sides. Place the shell on the foil-lined tray and bake until the shell is set, about 12 minutes. Remove the pan and set it on a wire rack and allow the crust to cool completely before filling it.

When the crust is cool, remove it from the tart pan and fill it with blood orange curd and chill it in the refrigerator until ready to serve. Garnish it with blood orange slices, dollops of whipped cream and mint sprigs, if desired. Tart will keep for 3 to 4 hours, filled with curd, but the crust may start to soften. Extra curd can be stored in the refrigerator in an airtight container for 3 to 4 weeks.