Make the crust: Combine the flour, confectioners' sugar, and salt in a food processor. Process briefly to blend. Add the chilled butter pieces and pulse until the butter is no bigger than small peas (about 1/4 inch). Add the egg yolk and drizzle the water over the mixture. Pulse briefly until the dough forms a loose ball. Dump the dough onto a large piece of plastic wrap and shape into a flat disk about 4 inches in diameter. Wrap the dough and refrigerate until well chilled, at least 1 hour or up to two days.
Lightly dust your work surface and rolling pin with flour. Roll the chilled dough into a 12-inch round. Lift and turn the dough several times as you roll to prevent sticking; dust the work surface and the rolling pin with flour as needed. Use a dough scraper or a spatula to loosen the rolled dough; carefully roll it up around the pin and unroll it over a 9-1/4-inch tart pan with a removable bottom. Gently fit it into the pan. Using lightly floured fingertips, gently press the dough into the corners and against the sides of the tart pan. Run the rolling pin over the top of the pan to trim the dough so that it's level with the top of the pan. Cover and freeze until the tart shell is very firm, at least 30 minutes.
Position a rack in the middle of the oven and heat the oven to 425°F. Line the frozen crust with foil and fill it with pie weights or a mix of raw rice and dried beans. Put the crust in the oven and immediately reduce the oven temperature to 400°F. Bake until the sides are golden and the bottom no longer looks wet, 15 to 20 min. Remove the foil, rice, and beans. Prick the bottom of the crust lightly with a fork (but don't pierce through it) and continue to bake until the shell is golden brown, another 5 to 8 min. Set the pan on a wire rack to cool while you prepare the filling. Reduce the oven temperature to 325°F.
Make the filling and finish the tart: In a medium bowl, whisk together the sugar, flour, lemon zest, and salt. Pour in the lemon juice and whisk until blended and the sugar is dissolved. In a small bowl, lightly beat together the eggs and vanilla and then add to the lemon mixture. Whisk until just blended. (Don't overwhisk or the filling will have a foamy top when baked.)
Pour the filling into the baked crust. Return the tart to the oven and bake until the filling jiggles slightly when the pan is nudged, about 20 min. Let cool on a wire rack until the tart is room temperature, about 1 hour. If not serving right away, chill it for 1 hour and then wrap it in plastic; refrigerate overnight or freeze. If serving immediately, remove the outer ring and run a long metal spatula under the tart to loosen. Carefully slide the tart onto a flat serving plate.
Clear a little space in the freezer. Chill the lemon tart for an hour, and then wrap it well and return it to the freezer for up to a month.
Make the strawberry sauce (optional): Put the strawberries in a food processor and pour the boiling water over them. Add the sugar and process until smooth. Serve immediately or refrigerate until ready to serve.
Let the tart cool in the pan to room temperature. Put the tart in the freezer for an hour to let it firm up, and then wrap it well in plastic and freeze it for up to a month. To serve, unwrap the tart, remove it from the pan, and set it on a flat serving plate. Let thaw at room temperature for about 1 hour.