Preheat oven to 350 degrees F. In a food processor combine flour, sugar and salt. Add butter and pulse until mixture resembles coarse meal. Turn mixture out onto a 9 by 13-inch baking pan and press into an even layer, covering the pan. Bake in the middle of the oven for 20 to 25 minutes or until layer is light golden brown. While the crust is baking, in a large bowl over simmering water whisk the butter, 3/4 cup sugar and lemon juice until the mixture feels warm, sugar is completely melted and incorporated, and is lighter, about 5 minutes. Remove bowl from heat. Beat eggs with 1 tablespoon sugar until light and frothy. Temper hot lemon mixture into eggs then add eggs back into lemon, whisking constantly. Pour lemon mixture over hot crust, return pan to the oven and bake another 15 to 20 minutes until curd is set and crust is golden brown. Allow to cool completely on a rack. Cut into 2-inch squares.