Sweet Pastry Crust:  In a separate bowl, sift or whisk together the flour and salt. Set aside. Place the butter in your mixer and beat until softened. Add the sugar and beat until light and fluffy. Gradually add the beaten egg, beating just until incorporated. Don't over mix or the butter will separate and lighten in color. Add flour mixture all at once and mix just until it forms a ball. Don't overwork or pastry will be hard when baked.  

Flatten dough into disk, cover with plastic wrap, and refrigerate about one hour or until firm.

Have ready an 8 - 9 inch (20 - 23 cm) tart pan with removable bottom. On a lightly floured surface, roll out the pastry into an 11 - 12 inch (28 - 30 cm) circle that is about 1/8 inch (3 mm) thick. To prevent the pastry from sticking to the counter and to ensure uniform thickness, keep lifting up and turning the pastry a quarter turn as you roll (always roll from the center of the pastry outwards to get uniform thickness). To make sure it is the right size, take your tart pan, flip it over, and place it on the rolled out pastry. The pastry should be about an inch larger than pan.

When the pastry is the desired size, lightly roll pastry around your rolling pin, dusting off any excess flour as you roll. Unroll onto top of tart pan. Never pull pastry or you will get shrinkage (shrinkage is caused by too much pulling of the pastry when placing it in the pan). Gently lay in pan and with a small floured piece of pastry, lightly press pastry into bottom and up sides of pan. Don't worry if there are cracks, simply patch with leftover pastry  Roll your rolling pin over top of pan to get rid of excess pastry. With a thumb up movement, again press dough into pan. Roll rolling pin over top again to get rid of any extra pastry. Prick bottom of dough (this will prevent the dough from puffing up as it bakes). Cover and freeze for about 20 minutes to chill the butter and to rest the gluten.

Meanwhile, preheat oven to 375 degrees F (190 degrees C) and place rack in center of oven. Line unbaked pastry shell with parchment paper or aluminum foil. Fill tart pan with pie weights, rice or beans, making sure the weights are to the top of the pan and evenly distributed over the entire surface. Bake crust for 20 minutes or until crust is dry and lightly golden brown. Remove weights and continue to bake for about 5 - 10 minutes or until the crust is cooked through and nicely browned. Remove from oven and completely cool the crust on a wire rack before filling.

Rhubarb Filling: Place the sugar and water in a large saucepan, over medium heat, and stir until the sugar completely dissolves. Add the lemon peel and cinnamon stick and bring to a boil. Add the chunks of rhubarb and reduce the heat to a low. Cover and simmer (about 5 - 15 minutes) until the rhubarb is tender and soft yet still keeps its shape (is not mushy). Remove the pan from the heat and let stand until the rhubarb has cooled to lukewarm. Then place the rhubarb in a strainer suspended over a large bowl. Once the rhubarb has drained, place the strained liquid in a small saucepan and boil until it is reduced by half. Let cool.

Cream Filling: In the bowl of your electric mixer (or with a hand mixer or wire whisk) beat the mascarpone cheese, heavy whipping cream, sugar and vanilla extract just until soft peaks form. 

To Assemble Tart: To remove the tart from the fluted sides of the pan, place your hand under the pan, touching only the removable bottom not the sides. Gently push the tart straight up, away from the sides. The fluted tart ring will fall away and slide down your arm. If you want to remove the bottom of the pan, run a knife or thin metal spatula between the crust and metal bottom, then slide the tart onto your serving plate.

Spread the cream onto the baked tart shell, smoothing it out with the back of a spoon or with an offset spatula. Arrange the rhubarb decoratively on top of the cream and then drizzle the syrup over the rhubarb. This tart should be eaten the day it is made. It does not keep well, even when refrigerated.

Serves about 8 - 10 people.