• In a large mixing bowl, add the softened butter and sugar. Beat with a stand mixer or hand mixer fitted with a dough hook until the mixture is creamy. Add the egg and vanilla extract, and mix until fully combined. In a separate bowl, whisk the flour and salt together, then add to the wet ingredients. Mix until a smooth dough forms. The dough should be soft but not overly sticky.
  ½ cups granulated sugar , ⅔ cups butter, 1 egg, 1 teaspoon vanilla extract , 1 pinch salt , 2 ¼ cups flour
• Transfer the dough to a floured work surface. Remove ¼ of the dough (for the streusel later) and store it in the fridge until needed. Divide the remaining dough into two parts. With floured hands, roll one portion into a log and press it around the edge of a greased pie dish or springform pan (use a 9-inch/23 cm pan). Press the dough up the sides to form a crust about 2 inches (5 cm) high.
  
• Roll out the remaining portion of dough and press it evenly into the bottom of the pan to form the pie base.
  

Prepare the filling

• Preheat your oven to 350°F (180°C).
• Rinse the rhubarb under running water and slice into ¾-inch (2 cm) pieces. No need to peel the rhubarb—the skin adds a beautiful red color.
  ½ cups sugar , 3 tablespoon corn starch, 1 teaspoon vanilla extract
• Place the rhubarb in a saucepan and mix in the sugar. Let it sit for about 10 minutes until it begins to release its juices.
• Stir in the cornstarch and vanilla extract. Bring the mixture to a boil and briefly cook for about 2 minutes, just until thickened. The rhubarb should not cook, we just want to bind the cornstarch.
  
• Pour the rhubarb mixture over the prepared crust. Crumble the reserved dough from the fridge over the top as a streusel.
  
• Bake in the oven for about 60 minutes. You can serve it cold or luke warm. Optionally pair it with whipped cream or vanilla ice cream.