Blind bake the tart crust and set aside to cool completely.
In a bowl, beat the unsalted butter, sugar, and salt until combined, then stir in the whole eggs and egg yolks one at a time. Add the grapefruit juice and zest and continue to mix.
Transfer the mixture into a pot on medium heat. Keep whisking the mixture until it thickens.
Pour the grapefruit curd into a clean bowl through a fine mesh sieve to remove any clumps that may have formed, as well as the zest.
Cover the bowl with plastic wrap and press the wrap onto the surface so the grapefruit curd doesn't form a film. Cool to room temperature.
Pour the cooled grapefruit curd into the cooled tart crust, and chill in the fridge for 1 to 2 hours.
While waiting for the tart to chill, segment the grapefruits.
Once the tart is chilled, decoratively lay out the grapefruits on top.