Heat oven to 350°F (175°C).

Combine the flour, salt, and sugar in the bowl of a food processor. Add butter and blend until the mixture forms large clumps. Set a marble or two of dough aside, and transfer the rest of it to a 9-inch round tart pan with a removable bottom, set on a large baking sheet. Press the dough evenly across the bottom and up the sides. Transfer to the freezer for 15 minutes, until solid.

Once firm, prick all over with a fork. Coat a piece of foil with nonstick spray and press it oiled-side-down tightly against the frozen crust, so it is tightly molded to the shape. Bake tart with foil (no pie weights needed) for 20 minutes, then carefully, gently, a little at a time, peel back foil and discard. If cracks have formed, use the marbles of dough you set aside to patch it. Return the crust to the oven for 5 minutes, until golden at edges and dry to the touch. Set the crust aside.

Place sugar and salt in a medium-sized pot and finely grate the zest of four lemons over it. Use your fingertips to rub the zest into the sugar and salt, releasing as much flavor as you can and breaking up the zest strips a little. Add eggs and whisk until evenly combined. Squeeze the lemons to make a strained 2/3 cup of juice and whisk juice into egg-sugar-zest mixture.

Transfer the saucepan to the stove and heat over low-medium, stirring constantly once the mixture begins to warm, until thickened, about 5 to 10 minutes. Add butter, a piece or two at a time, and stir until melted. Remove from heat and pour into the tart crust.

Bake for 15 minutes or until the filling is mostly set. Chill the tart completely in the fridge; it will finish setting once cool.

Gently push up on the bottom of the tart pan to pull down the sides of the pan. Transfer the tart to serving plate and cut into wedges. Serve with dollops of whipped cream and fresh berries.