Grease and line the rimmed tray with parchment or use two 8-inch/20cm Ø baking pans or cake rings. For the meringue: in the stand mixer fitted with the whisk attachment, beat egg whites along with the cream of tartar and a third of the sugar on medium speed.
Meanwhile, sift powders together. In a deli container, combine pistachio paste with the oil.
Increase mixer speed to high speed. Continue beating egg whites adding remaining sugar gradually until stiff peaks is reached.
Lower mixer speed, and add the egg yolks into the meringue at once. Preheated fan oven at 330ºF/160ºC.
Increase mixer speed for about 10 seconds toward the end.
Fold in the sifted powders, then add the pistachio-oil mixture and the toasted pistachios.
Spread batter onto the prepared baking tray.
Cake rings or molds...
Baking
Bake pistachio biscuit sheet for 30 minutes. Let cool and refrigerate or freeze overnight before using. To un-mold: run a small offset spatula around the borders, top with parchment and tray – reverse.
Bake pistachio biscuit for 35 minutes in baking pans or cake rings. Let cool off 10 minutes, de-mold and refrigerate overnight before slicing.
Storage
Biscuit, sponge and genoise can all be done in advance. Store for up to 3 days in the refrigerator or for up to 3 months in the freezer.