Every celebration should end with a delicious dessert. For Passover, an unleavened Chocolate-Walnut Cake with Orange is sure to satisfy that need.
Cake: Preheat oven to 350 degrees. Brush bottom and sides of an 8-inch square cake pan with oil. Line bottom with parchment, leaving a 2-inch overhang on 2 sides. Brush parchment with oil.
In a large bowl, whisk together matzo meal, ground walnuts, sugar, cinnamon, salt, and zest. Stir in oil, egg yolks, and orange juice.
In a mixing bowl, beat egg whites on low speed until foamy, 1 minute. Increase speed to high; beat just until stiff (but not dry) peaks form, 1 to 2 minutes more. Stir one-third of whites into batter, then fold in chopped chocolate. Gently fold in remaining whites (do not overmix). Transfer batter to prepared pan.
Bake until cake is golden on top and springs back when lightly pressed, 25 to 30 minutes. Let cool in pan 10 minutes. Remove cake using parchment and transfer to a wire rack; let cool completely.
Serving: Place cake on a platter. Drizzle with melted chocolate; top with orange rounds and walnuts.