In a large mixing bowl, add in the butter, powdered sugar, and granulated sugar. Using a hand mixer, beat on medium until combined.
Add in the vanilla extract and egg yolk. Beat until incorporated. Scrape down the sides.
Add in the flour and salt. Mix until the flour is mixed into the wet ingredients and a ball of dough forms.
Press the dough into a non-stick 9-inch tart pan. Press it evenly into the bottom and sides of the pan. I don't recommend using a ceramic dish like mine in the photos, it's almost impossible to get slices out of it.
Place into the oven and bake for about 25 minutes until the edges are golden brown and the center is slightly puffy.
Remove from the oven. Using a spoon, press the dough down in the bottom of the pan and up on the sides. You can also cover the inside with tin foil and weigh it down with dried beans or standard pie crust weights.
Let cool and begin working on the curd.
In two bowls, divide the egg whites and yolks. Set aside the egg whites from another recipe.
In a medium saucepan, add in the sugar, salt, and cornstarch. Whisk until combined.
Add in the pichuberry puree and whisk until incorporated into the sugar mixture. Place saucepan over medium heat and let it come up to a boil. Whisking occasionally.
Once it comes up to a boil, let it boil for 2 minutes. Whisk constantly to avoid burning.
Pour about ½ cup of the sugar and puree mixture into the egg yolks and immediately beginning whisking. You want to whisk immediately to avoid cooking the yolks. This is tempering the yolks.
Add the tempered yolks into the saucepan with the remaining sugar and puree mixture and whisk until incorporated.
Let the pichuberry curd come up to a boil and boil for about 5 minutes until thickened. Be sure to whisk pretty constantly to avoid burning.
Remove from the heat and add the cold butter. Whisk until the butter is melted and well combined.
Strain the mixture to get out any cooked bits of egg. I strained mine straight into the cooled tart crust. Tap the pan to smooth out the curd.
Immediately place the tart in the fridge to cool down and set up.
Before serving, add the whipped cream on top.
Place the heavy cream and powdered sugar in a large mixing bowl. Using a hand mixer, beat until stiff peaks form.
Add the whipped cream into a piping bag fitted with a 1M tip. Pipe different size stars on top of the tart.