How to Make It
Roll pie dough to a 1/8-inch thick circle and place inside a greased 9-inch metal tart pan or pie pan. Cut excess dough, leaving a 1/2-inch overhang. Fold overhang under itself, creating a thicker ring of crust around the pie’s edge. Crimp edge. Take a sheet of aluminum foil and grease it liberally with butter. Place the buttered surface inside the pie shell, allowing the pie dough to come in direct contact with the aluminum foil. Freeze crust for 1 hour or overnight. Preheat oven to 350°F. Bake crust with aluminum foil for 25 minutes. Remove aluminum foil and use a spoon to press down any areas that have puffed up. Bake uncovered for an additional 5 minutes. Remove and set aside to cool.
In a mixer fitted with the whisk attachment, combine butter and 2/3 cup sugar on medium-high until well combined, about 3 minutes. Scrape down sides of bowl with a spatula and add almond flour; beat to incorporate, about 2 minutes. Add flour and cornstarch, and mix to combine. Scrape down sides of bowl again; add egg, orange zest, and vanilla, and beat on high for 1 minute.
In a large bowl, toss cut rhubarb with orange juice and remaining 1/3 cup sugar. Set aside.
In the cooled crust, evenly spread almond-orange filling. Lift the rhubarb segments out of any juice in the bowl, and place them on top of the almond cream in a single layer.
Bake until almond filling has puffed, turned golden, and no longer jiggles in the center when lightly shaken, about 1 hour. Allow to cool completely before slicing.