In a food processor fitted with a steel blade, combine all theingredients until they form a solid mass that rises above the blade. You can add extra water by the tablespoon if the mass does not congeal within the first minute. Tiny pieces of butter should still be visible in the dough when it's done. Remove the dough from the bowl and work it quickly into a ball on a lightly floured surface. Cover with plastic wrap and refrigerate for at least half an hour.
After the dough has rested in the refrigerator, roll it out on a lightly floured surface until it forms a circle approximately 13" in diameter. Center the cirlce of dough in a 10-inch tart pan with a removeable bottom. Use your knuckles to make sure that the dough tucks neatly against the edge of the pan and run the rolling pin around the rim to remove the excess. Cover and refrigerate again for at least half an hour.
Line the tart shell with aluminum foil, being careful.ingredients to cove the edges. Pierce the aluminum and the dough several times with a fork and fill the shell with dried lentils. Bake for 20 minutes. Remove the aluminum and the lentils and continue baking until the shell is golden brown, about 15 minutes more.