Step 1

Preheat the oven to 350 degrees F.

Step 2

For the crust: Pour the graham cracker crumbs into a bowl and stir in the melted butter and sugar. Press the mixture into a 9-inch tart pan with a removable bottom and bake until golden and set, about 5 minutes. Set aside to cool slightly.

Step 3

For the filling: Mix the condensed milk, egg yolks and grapefruit zest and juice in the bowl of a mixer, then mix on high until smooth and thick. Add a few drops of the food coloring, if using, to give it a ruby grapefruit color, and stir thoroughly to combine.

Step 4

Pour the mixture into the crust and bake until set, about 15 minutes. Allow to cool, then refrigerate for at least 1 hour. Serve with whipped cream.