1 3⁄4 cup graham cracker crumbs
3 Tablespoons granulated sugar
1⁄4 teaspoon salt
1⁄3 cup unsalted butter, melted
1⁄3 cup unsweetened coconut flakes
1⁄4 cup toasted coconut flakes
2 Tablespoons chopped pistachios
2⁄3 cup sugar
3 Tablespoons cornstarch
1 1⁄2 cups grapefruit juice
3 large egg yolks, whisked
6 Tablespoons butter, cut into cubes
1 drop red food coloring (optional)
Heat oven to 400 degrees F. Grease a long rectangular tart pan (or a 9-inch round tart or quiche pan) and set aside. Combine the graham cracker crumbs, sugar , and salt in a bowl or food processor. Pulse until combined. Drizzle in melted butter and mix or pulse until mixture looks like wet sand. Transfer to a bowl and mix in coconut. Press into the bottom of the prepared pan. Bake until set, about 5 to 8 minutes, or until lightly browned. Transfer to a rack and let cool completely.
In a medium saucepan, combine sugar, cornstarch, and juice. Mix well and heat to medium heat. Cook, stirring, until thickened and bubbly. Gradually and slowly whisk in half of the hot mixture into the egg yolks (important so the eggs don’t scramble). Add egg mixture to the saucepan and cook, stirring constantly until the mixture thickens, about 2 to 3 minutes. Remove from heat and add in the butter cubes; whisk until melted. Stir in food coloring (optional).
Pour the mixture into the cooled crust and smooth the top with a spatula.. Cover with plastic wrap pressed against the top of the top and chill for at least 4 hours, preferably overnight, to set. To serve, top with coconut flakes and pistachios.