1. Preheat the oven to 400°F. Prepare the Basic Butter Pastry. Roll out one-half of it between lightly floured sheets of wax paper to make an 11-inch round. (Freeze the other half for another use.) Fit the round into a 9-inch tart pan with a removable bottom, press it against the sides of the pan, and trim off any overhanging pieces. Pierce the bottom and sides of the pastry thoroughly with the tines of a fork. (This will prevent the crust from puffing up.) Bake the crust for 10 to 12 minutes, or until it is dark golden.

2. Stir together the sugar, cornstarch, and salt in a small saucepan. Gradually stir in 2/3 cup water. Add ¾ cup blueberries and cook over medium heat, stirring constantly, until the mixture comes to a full boil, the berries have popped, and the sauce has thickened. Remove from the heat and stir in the lemon zest and lemon juice.

3. Combine the thickened sauce with the remaining 3¼ cups blueberries in a medium bowl; transfer to the baked tart crust and spread the blueberries to fill the shell. Let cool to room temperature and serve, or cover and refrigerate until ready to serve. The tart will keep in the fridge for 3 days.