In your mixer bowl add butter and sugar and beat until fluffy.
Add the egg, thyme, and vanilla, to the butter and sugar mixing thoroughly.
Add the flour to the mixture a little at a time until. Make sure not to over mix the dough. Just mix it until it begins to come together and all of the flour is incorporated.
Remove dough from bowl and form it into a ball (do not overwork the dough or it will be tough). Flatten into a disc and wrap in plastic wrap. Refrigerate for 30 minutes to firm up dough.
Once the dough is ready lay it on a lightly floured surface. Roll it out to approximately 1/8” thickness and make sure it is slightly larger than your tart pan (give it an extra inch all the way around).
Lay the dough over the tart pan. DO NOT stretch or pull the dough to make it fit, this will cause it to shrink when it is baked. Instead of pushing the dough down into the pan use your fingers to work the dough up the sides of the pan.
Pierce the bottom of the dough with a fork and place foil in the center then fill with pie weights (I use dried beans). This will keep the dough flat as it bakes.
Refrigerate for 15 – 20 minutes to let the dough firm back up.
Bake in a 400°F oven for 15 minutes, then remove the pie weights and continue baking until the crust is golden brown.
Remove from the oven and let cool completely.
Juice 2-3 grapefruits and pour juice through strainer to remove any pulp or seeds.
Add grapefruit juice to a small pan and bring it to a boil to reduce the liquid by half.
Add the sugar to the grapefruit juice, stirring to dissolve.
Let the juice cool slightly before placing it in a bowl over a pot of simmering water (or in a double boiler)
Add the eggs, egg yolks and grapefruit zest, whisking constantly for 10-15 minutes. The curd should become thick like pudding.
Once thickened remove it from the heat and add the butter stirring it in until it is completely incorporated.
Let the curd cool slightly before placing a piece of plastic wrap on the surface of the curd to keep it from developing a skin. Then place it in the refrigerator until completely cool.
Once the curd has cooled and firmed up add it to the tart and put it in the refrigerator to firm up overnight. Again, cover it with plastic wrap so the curd doesn’t develop a skin.
Peel a grapefruit and break it into sections. Remove the thin membrane from each section then thinly slice the piece of fruit. Before serving add the slices to the top of the tart.