Rhubarb tarte fine with lavender

Instructions

• Prepare the dough
• In a medium-sized mixing bowl, stir together the flour and the salt. Add in the cubes of butter and using a pastry cutter or a pinching motion with your hands, quickly mix in the butter until it has slightly decreased in size (about 25% smaller than the original cubes).
• Add in the ice water and mix until the dough comes together into a shaggy ball. On a lightly floured surface, pat the dough into a rectangle. Roll the dough into a 10″ x 5″ rectangle. Take the short end and fold it into the center. Fold the other short end on top so that the long sheet has now been folded into thirds like a letter.
• Rotate the dough so that the long end faces you and the short ends (where you can see the fold) are on the left and right sides. Roll out into another 10″ x 5″ rectangle. The short ends where you can see the fold should be the 5″ sides of the rectangle. Fold into thirds again and then turn so short ends are on the left and right sides again.
• Do this process of rolling out, folding into thirds, and turning 2 more times. Work relatively quickly so the butter doesn’t get too warm. It’s okay if you see butter pieces in the dough and if your rectangle is just approximate and the edges are not perfect. Each time you fold and roll, the dough should be a bit smoother.
• Wrap the dough in plastic wrap and refrigerate for 2 hours. Remove the dough from the fridge. Let rest at room temperature for 10-20 minutes if it’s too stiff to roll out right away. Repeat the process of rolling into a 10″ x 5″ rectangle, folding in thirds and doing a turn of the dough two more times. Cover and return to the refrigerator for at least 1 hour.
• Prepare the topping
• First make the lavender sugar by mixing together the lavender and the 4 Tbsp of sugar in a small food processor until the lavender is finely ground. Alternatively, you can grind the lavender separately in a spice grinder or chop it very finely by hand, and then use your fingers to rub it into the sugar to help release its flavor. Set the sugar mixture aside.
• Remove the dough from the fridge. Let rest at room temperature for 10-20 minutes if too firm to roll out.
• Meanwhile,  In a small bowl, stir together the ground pistachios, 1 Tbsp of the lavender sugar, and 1 Tbsp of flour. Preheat the oven to 400F.
• On a well-floured surface, roll the dough into a large circle of at least 12-inches in diameter. Trim the dough into a perfect 12-inch circle by tracing around a 12-inch pan or dish. Gently fold the dough in half and transfer to a parchment lined baking sheet. Refrigerate while you prepare the rhubarb.
• Trim the ends off the rhubarb (but do not throw them out). Cut the rhubarb into very thin slices, about 1/8-1/4-inch thick, making sure to cut at an angle–if you cut straight down, it may be more fibrous. Remove the dough from the fridge. Add the pistachio mixture to the bottom in a thin layer, leaving a 1/4-inch border. Arrange the rhubarb slices on top in tightly packed concentric circles, overlapping them generously, since the rhubarb will shrink considerably. Brush with the melted butter and sprinkle with the remaining 3 Tbsp of sugar. It may seem like a lot but trust me, the dessert is still very tart from the rhubarb.
• Bake for 25-30 minutes until the crust is a nice golden brown. While the dessert is baking, add in any leftover slices of rhubarb, along with their ends, to a small saucepan. Add the water and 1/3 cup of sugar. Boil for about 20 minutes, stirring occasionally until the mixture is very thick and has reduced significantly. Strain out the rhubarb. Once the tart has come out of the oven, wait 5-10 minutes and then brush generously with the syrup. The dessert is best served on the day that it is made, while the pastry is still nice and crisp.