Step 1Place the pine nuts in a food processor and pulse a few times. Add the sugar and flour and continue to pulse until the nuts are finely ground.
Step 2Place the nut mixture in a mixing bowl and add the butter, egg and vanilla. Beat with an electric mixer or by hand until thoroughly combined.
Step 3Divide the dough into 3 parts. Wrap each piece in plastic wrap. Freeze 2 pieces for future use and refrigerate the third piece for at least 10 minutes before using.
Step 4Heat the oven to 350 degrees. Generously butter and flour a 9-inch fluted tart pan with a removable bottom and refrigerate it while the oven heats.
Step 5Remove the tart pan from the refrigerator and use your fingertips to press the chilled dough over the bottom and up the sides of the pan. Trim off excess.
Step 6Bake the crust for 10 to 15 minutes, then rotate the shell and continue baking until golden brown, another 10 to 15 minutes. Remove the shell from the oven while you make the filling. There may be some cracks in the shell. They will not affect the tart.
Step 1Bring about 1 1/2 inches of water to a boil in a pot that is slightly smaller than the diameter of the mixing bowl you will be using for the sabayon.
Step 2Meanwhile, in a large metal bowl, whisk the eggs, yolks and sugar until smooth, about 1 minute.
Step 3Set the bowl over the pot so that it's not touching the water, and, using a large whisk, whip the mixture while you turn the bowl, for even heating. When the eggs are foamy and have thickened, about 2 minutes, add one-third of the lemon juice. Continue to whisk vigorously and when the mixture thickens again, add another third of the lemon juice. Whisk until the mixture thickens again, then add the remaining lemon juice. Continue whisking vigorously, still turning the bowl, until the mixture is thickened and light in color, and the whisk leaves a trail at the bottom of the bowl. The total cooking time should be about 8 to 10 minutes.
Step 4Turn off the heat, but leave the bowl over the water as you add the butter, whisking in, one tablespoon at a time. The sabayon may loosen slightly, but it will thicken and set as it cools.
Step 5Pour into the tart shell and place on a baking sheet. Heat the broiler. While the sabayon is still warm, place the tart under the broiler. Leaving the oven door open, brown the top of the sabayon, rotating the tart if necessary for even color, about 20 to 30 seconds. Keep an eye on the tart so it doesn't burn.
Step 6Remove the tart from the oven and let it sit at least 1 hour before serving at room temperature or chilled.