To prepare crust, weigh or lightly spoon 4.5 ounces (about 1 cup) flour into a dry measuring cup; level with a knife. Combine 4.5 ounces flour, 2 tablespoons sugar, 2 tablespoons unsweetened cocoa, and 1/4 teaspoon salt in a food processor; pulse 2 times or until blended. Add shortening and chilled butter; pulse 6 times or until mixture resembles coarse meal. With processor on, slowly pour ice water through food chute, processing just until blended (do not allow dough to form a ball); remove from bowl. Gently press mixture into a 4-inch circle; wrap in plastic wrap. Chill 30 minutes.
Preheat oven to 350°.
Unwrap and place chilled dough on plastic wrap. Lightly sprinkle dough with flour; roll to a 10-inch circle. Fit dough, plastic wrap side up, into a 7-inch pie plate coated with cooking spray and parchment paper. Remove remaining plastic wrap. Fold edges under, and flute.
To prepare filling, place 3 tablespoons butter and chocolate in a microwave-safe bowl. Microwave at HIGH 30 seconds or until butter and chocolate melt, stirring well to combine. Fold the Nutella into the chocolate mixture. Place vanilla and egg whites in a bowl; beat with a mixer at medium speed until foamy. Gradually add 1 cup sugar; beat until soft peaks form (about 2 minutes). Gently fold melted chocolate mixture into egg white mixture. Gently fold in the Chobani Greek Yogurt.
Lightly spoon the 1 cup flour and 1/3 cup Dutch process cocoa into dry measuring cups; level with a knife. Sift the flour, cocoa, baking powder, and dash of salt in a small bowl. Fold flour mixture into egg white mixture. Pour mixture into prepared crust. Bake at 350° for 40 minutes or until a wooden pick inserted in center comes out clean (because the topping becomes so hard, it is difficult inserting a toothpick into the top to see if it is done. I baked mine for about 40-42 minutes). Cool on a wire rack.