On a floured surface, roll out your dough into a circle about 1/8 inch thick. Transfer it to your pie plate and trim it to about half an inch beyond the rim. Flute the edges beautifully and pop it in the refrigerator for about 30 minutes. Meanwhile, preheat your oven to 425°.

Once chilled, line your crust with double-thick foil. Fill it with pie weights, dried beans, or uncooked rice to prevent bubbling. Bake on the lower rack of your oven until the edges are golden brown—this should take around 20 to 25 minutes. After removing the foil and weights, bake again until the bottom is golden brown (around another 4 minutes). Let it cool completely on a wire rack.

In a large saucepan, combine sugar and cornstarch. Stir in grapefruit juice and water until smooth. Cook over medium-high heat while stirring until thickened and bubbly—it should take just a few minutes! Reduce heat and continue cooking while stirring for another two minutes before removing from heat.

Take half a cup of hot filling and stir it slowly into your beaten egg yolks—this helps temper them so they don’t scramble when added back into the pan. Return everything back to your saucepan while stirring constantly. Bring it back to a gentle boil then cook while stirring for two more minutes before removing it from heat again. Gently fold in butter and lemon extract before pouring this filling into your cooled crust.

In a separate bowl, beat egg whites along with cream of tartar on medium speed until soft peaks form. Gradually add sugar one tablespoon at a time while beating on high speed until stiff glossy peaks form. Spread this meringue evenly over your hot filling, making sure to seal those edges well against the crust.

Finally, bake at 350° until your meringue turns golden brown—this will take about 12 to 15 minutes. Once done, let cool on a wire rack for an hour before refrigerating for at least three hours before serving.