3 cups sugar
Zest of 3 grapefruits finely grated
2 cups flour
12 tablespoons (1& 1/2 sticks) unsalted butter, cut up
pinch of salt
1 cup & 2 tablespoons freshly squeezed lemon juice, strained (about 8 lemons)
In processor blend sugar and zest for 1 min. Scoop out 1/4 cup of blended sugar into small bowl. Scoop 2 & 1/4 cups sugar into large bowl. Combine 1&1/2 cups flour, salt, into remaining 1/2 cup of sugar. Blend. Drop in butter. Pulse many times. Mixture will look like sand, then big clumps.
Dump clumps into 13 x 9 inch baking pan. Press into bottom of pan. Slide into 325 degree oven & bake til golden, about 25 mins.
Whisk remaining 1/2 cup flour into the large bowl with other sugar. Whisk in juice and eggs. When pastry is golden, remove, turn down oven to 300 degrees pour egg mixture over pastry & bake 30 mins.
After 30 mins,remove from oven & spread remaining 1/4 sugar over top. Cool. Chill. Cut into squares.